Seakeeping Models

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Seakeeping Models

Fossen, Thor I

The study of ship dynamics has traditionally been covered by two main theories: maneuvering and seakeeping. A chief distinguishing characteristic of these theories is the use of different coordinates and reference systems to express the equations of motion. This chapter presents the seakeeping theory and the classical equation in naval architecture which is transformed from equilibrium axes {s} to body‐fixed axes {b} using the time‐domain solution known as the Cummins equation. For most problems related to ship motion in waves, potential theory is sufficient to obtain results with appropriate accuracy for engineering purposes. Frequency‐dependent hydrodynamic forces can be determined experimentally or computed using potential theory programs or seakeeping codes. The chapter describes the transformations needed to obtain what is called the frequency‐domain model and a method known as forced oscillations. The time‐domain models are useful both for simulation and control systems design.