In general, the speed power performance of ships is optimized for design speed and draught in accordance with the contract condition. But, the contract condition may not be always the same as the actual operating condition. Therefore, in order to reduce the fuel consumption practically, it is necessary to optimize the performance under various conditions considering the actual voyage. This is the reason that the trim optimization covering various operating profiles becomes the main issue in reducing fuel oil consumption.
In this paper, a numerical study is carried out to optimize trim conditions through the computational evaluation system called SoLuTion developed by Samsung Heavy Industries Co. (SHI) with variation in draught, ship speed and voyage trim. In order to get more accurate results in resistance and self-propulsion performance, the Reynolds-Averaged Navier-Stokes (RANS) equations including Volume of the Fluid (VOF) method by Hirt and Nichols (1981) for free-surface boundary condition and moving mesh technique for propeller rotation effect are employed as governing equations. Reynolds Stresses Model (RSM) with the wall function is applied as a turbulence model for turbulent flow computation.
Through this study, the followings are the main three factors to be considered in evaluation of the quantitatively accurate speed performance by varying the draught, speed and voyage trim. First, the distance from hull surface to the first grid point should be adjusted to eliminate the effects of frictional resistance. Second, the grid system should be generated to avoid the grid dependency on variation of draught. Finally, the running trim and sinkage of the voyage conditions should be considered. The results of the trim optimization performed numerically are well-matched with the towing test results conducted at Samsung Ship Model Basin(SSMB). As the results of this study, it is confirmed that SoLuTion is a useful and efficient tool for trim optimization and the provided optimum trim will be able to contribute to fuel savings under the operating conditions. From trim optimization study, it is found that there is certain level of effects due to the bulb and transom immersion to find the optimum trim condition. Also SoLuTion is applicable not only to trim optimization but also to parametric studies in optimum shape of the ships considering the actual operating profile.
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