STOPPING SIMULATIONS AND SEA TRIAL MEASUREMENTS OF A SHIP WITH DIESEL-ELECTRIC PROPULSION AND CONTROLLABLE PITCH PROPELLERS

摘要

The particular combination of diesel-electric drives and variable-pitch propellers opens new possibilities for the optimization of stop maneuvers with the goal of shortening the stop distance and of reducing the substantial load of the individual components of the propulsion system. An important issue during stopping is the so-called wind-milling effect. In this case the torque becomes negative and the propeller is driven by the water. The electric motor works as a generator, which can have strong negative influence on the stability of the electric board net. Furthermore over speed conditions have to be avoided to protect the mechanical components like gearbox and rotor of the electric motor. The optimal combination of the pitch setting and number of revolutions during the different stages of the stop maneuvers allows the reduction and in some cases the elimination of the wind-milling stage of the maneuver. A simulation method is developed to simulate the stopping behavior of ships equipped with diesel-electric propulsion and controllable pitch propellers (CPP). The motion behavior is calculated by solving the equations of motion in time-domain. The velocity dependent resistance force of the hull is approximated by a cubic polynomial based on measured data of the resistance model test. The rudder forces are estimated with semi-empirical formulas. Thrust and torque of the propellers follow from the open water diagram of the propeller. The developed method is applied for a 96.6 m long seismic research ship equipped with a diesel-electric engine and two CPPs. Various simulations were performed and compared to sea trial measurements. The investigated scenarios include variations of the rate of rotation of the propeller and of the pitch angle. A satisfactory correlation was found between the simulations and the measurements that were taken. Wind-milling can be predicted reliably.