Effects of water depth and speed on ship motion control from medium deep to very shallow water

摘要

To extend the knowledge on ship manoeuvring and predict ship's behaviour accurately from medium deep to very shallow water, this paper comprehensively investigates water depth and speed effects on ship's manoeuvrability, steering model and motion control through experimental studies. Free running model tests at four water depths and six speeds were conducted using a scaled ship model in the towing tank at Flanders Hydraulics Research (FHR). The influence of under keel clearance and speed on the acceleration tests and zigzag manoeuvres were firstly analysed. Secondly, the shallow water effect on ship steering model was discussed via theoretical analysis and experimental validation. Then, the investigation of the effects of speed and under keel clearance on the ship motion controller's parameters and performance was executed, and a novel adaptive controller was proposed. To improve controller's performance in shallow water, a scheme was proposed to optimize its parameters. The results indicate that both speed and water depth have considerable influence on ship's manoeuvrability and controllability. Especially, water depth restrictions change the hydrodynamic forces, reduce the propulsion efficiency and manoeuvreability, the ship becomes more difficult to manoeuvre and control in shallow water. These impacts on ship manoeuvring, modelling and motion control cannot be neglected.