Numerical Simulation of Trim Optimization on Resistance Performance Based on CFD Method

In response to the gradually stringent carbon emission requirements of the International Maritime Organization (IMO), the energy-saving methods of the shipping industry have received increasing attention. Today how to reduce fuel consumptions so as to lower carbon emissions to improve the economic and environmental benefits of ships has become a hot topic. As one of the most easily implemented energy-saving methods, trim optimization has caught more and more researchers’ eyes. In this paper, a commercial CFD software STAR-CCM+ was adopted to analyze the influence of trim on the resistance performance of VLCC ship mainly with fixed model method under various typical conditions of the design draft and the ballast draft respectively. The grid convergence was studied at the design draft and the typical numerical simulations were verified by the experimental results before carrying out various numerical simulations of trim optimization. Seven different kinds of trim conditions, which correspond to the changing process of the full scale ship from trimming by stern 4m to bow 4m, were simulated with 3 different speeds of design draft and ballast draft. The changes of total resistance, frictional resistance and residual resistance were analyzed to explore the effect of trims on the ship’s resistance. The variation of ship’s wetted surface area and waterplane area under different trim angles were studied. It was found that under the condition of low Froude number, both the simulation of free trim and sink method and the fixed model method can achieve good accuracy with the method of fixed model reducing the simulation time obviously. Both conditions of the design draft and ballast draft had a certain reduction effect of total resistance for trimming by bow properly, of which the change of frictional resistance is dominant in the decrease of total resistance at design draft while the change of residual resistance is the main cause at ballast draft. The optimum trims were found and the optimal total resistance reduction effects were evaluated. The optimal total resistance reduction effect increased with speed whether at the design or the ballast draft and the reduction effects were more obvious at ballast draft. Meanwhile, it was found that the changes of wetted surface area and the waterplane area with different trims were close to the variation tendency of the frictional resistance.