This paper presents a CFD simulation to study the ventilation phenomenon of tunnel thrusters in dynamic positioning (DP) mode of a typical North Sea shuttle tanker consisting of two main propellers, two rudders, and two bow tunnel thrusters. Measurements of blade thrust and moment for the propeller shaft (corresponding to propeller torque) with ventilated propellers at different submersion positions are presented and discussed. Additionally, in order to obtain insight into the effect of waves on ventilation which further affects propeller loading and dynamic fluctuations, simulations of a tunnel thruster are performed at different immersion ratios.
This paper also presents and discusses the factors in the evaluation of thruster performance, such as, the extent of present knowledge for tunnel thrusters as related to ahead ship speed, and interaction between thruster jet flow and the mainstream with various drift angles. Moreover, thrust degradation of tunnel thrusters is considered in the thrust allocation algorithms for the DP capability calculation.
The objective of this study is to understand the dynamics of thruster forces. In addition, results of the study provide knowledge for a robust thrust allocation algorithm for dynamic positioning capability assessment.