Efficient simulation of ship maneuvers in waves

Abstract The description of ship motion dynamics is typically divided into two separate categories of inquiry: maneuvering in calm water and seakeeping at straight course. Combining both fields of investigation is not a trivial process because the hydrodynamic forces function differently. This thesis reports on the development of two numerical models to simulate the maneuvering motion of ships in waves. In order to simulate the motions, a precise description of the forces is necessary. In both approaches, the rudder forces are calculated with state-of-the-art procedures. For the propulsion, a numerical model is developed based on the propeller openwater diagram. An engine model is developed to determine the propeller rate of rotation for diesel-electric engines. A comparison with sea trial measurements reveals a very satisfactory representation of the propulsion and engine characteristics with the numerical model. The hydrodynamic forces acting on the hull are generally dependent on the motion frequency. Hence, the seakeeping motion is often solved in frequency domain. For the maneuvering case, the zero-frequency hydrodynamic forces are of interest. A two-time scale model is introduced that divides the basic motion equations into two groups - the zero-frequency maneuvering motion and the high-frequency wave-induced motion. Each group is solved separately and certain parameters are exchanged. Additionally, a unified theory is presented. This approach unifies both theories by extending the seakeeping theory. It is based on the impulse-response function, in which the retardation functions are built up for the entire motion frequency range and integrated during the time simulation over the elapsed time. The zero-frequency damping forces are incorporated into the retardation functions or added directly to the motion equations during time domain. They are calculated either with the slender-body theory or taken from the literature. A validation with experimental data from the literature is conducted with both methods. The simulated turning circles of the S-175 container ship and the KVLCC2 tanker in regular waves show satisfactory agreement with the measurements for both theories. Both methods capture the maneuvering motion in waves as well as the wave-induced motion during turning. Slight differences between the two models occur in the average track due to additional nonlinear effects in the unified theory. The simulated oscillatory wave-induced motion is very comparable between the two theories and shows reasonably well agreement with the measurements.