In the present work, ship propulsion performance at different trim angles are investigated. CFD method with dynamic overset grid technique is used to direct simulate the free running ship model. The self-propulsion with design ship speed Fr=0.20 is firstly conducted and the predicted results are compared with experimental data. Then ship with different trim angles varying from -0.8° to 1.6° are simulated to investigate the propulsion behavior at different trim condition. All the numerical simulations are carried out by CFD solver naoe-FOAMSJTU. Hydrodynamic forces including thrust and torque of twin propellers are analyzed. It is found that the thrust and torque have much different behavior at negative and positive trim angle. The corresponding wake flows at different trim angles are responsible for the above propulsion characteristics.

INTRODUCTION

Recently, the performance of ship propulsion, especially for the efficiency of propulsion, has become a very hot topic due to the strict terms proposed by International Maritime Organization for the newly built commercial ships to meet the increasing requirement of Energy Efficiency Design Index (EEDI) regulations. Thus, it is of great importance to find a suitable and reliable approach to evaluate the ship propulsion performance under various conditions. Generally, ship propulsion is closely related to resistance and the propeller performance. In order to evaluate a ship's propulsion performance, firstly we need to have the ability to estimate the behavior of ship hull-propeller interaction, and another important aspect is the resistance prediction at different conditions. Both the above two aspects can contribute to improve the efficiency of ship propulsion. For the hull-propeller interaction, it is very essential to have an accurate prediction model of the hydrodynamic forces of self-propelled ship to see whether the reduction of power will affect the performance of ship propulsion. For the ship resistance, ship trim optimization will have a good influence on the hydrodynamic forces of ship hull and further finding a propriate position to reduce the resistance. Therefore, trim angle effects on the ship propulsion should be draw more attention.

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