Full 6-dimensional modelling - a new approach for full-mission simulations

The newly developed full 6-dimensional method is based on the adding and coupling of the first order wave forces and calm-water manoeuvring forces. A method is developed to overcome the discrepancy between the potential theory used in calculating the forces due to waves and the viscous phenomena affecting the manoeuvring forces. The motions of the vessel are calculated with the well-known equation of motion. Traditionally, ship manoeuvring models are based on a 3, (3+1) or 4-degrees of freedom mathematical model, later enhanced to 6 degrees of freedom. In these models superposition of motions due to waves and calm-water manoeuvring takes place. The main benefit of the full dynamic 6-D modelling is the superposition of the forces in the equation of motion. Therefore external forces (due to for instance a towline and winch in case of an escorting tug) can be included in the equation of motion with a more realistic behaviour as a result. A theoretical background will be given on the new 6-D method. The coupling of the calm-water manoeuvring model based on the mathematical Abkowitz model and the seakeeping model will be explained. The origin of the different components used in the equation of motion is given. The 6-D model has been validated for an ASD-tug. The results are compared with model test results. This new way of modelling ship motion behaviour is an elegant and attractive method to simulate towing scenarios and to execute tug-operability studies.