Utilization of CFD tool for ship trim optimization analysis

Numerical prediction through Computational Fluid Dynamic (CFD) for ship design and optimization has been applied in the recent years in the ship industries. Nowadays, there are several commercial software with Graphic User Interface (GUI) that is convenient to use. SHIPFLOW by FLOWTECH International AB is designed towards naval architect with an easy to use GUI for CFD predictions. There are three methods that can be used to predict ship’s resistance in SHIPFLOW, which are Panel method, Boundary layer method, and Reynolds-average Navier Stokes (RANS). In this thesis, all three methods are going to be used with some exceptions. The effect of free surface is neglected for viscous flow with RANS method and only one type of fluid being considered. This limitation will in turn neglect the wave breaking and spray (bulb effect) that are of a viscous effect. Turbulence model used to solve the equation in RANS method is only using Explicit Algebraic Stress Model (EASM). There are two type of ship that is considered for this study, which are tanker ship and RORO vessel. There was an issue with the software when running simulation for RORO vessel at draft lower than 7.7 meter. Looking at the mesh, it seems that the software encountered an error when the bulb is not fully submerged or the top part of the bulb is too close with the surface. In general, CFD global RANS gives accurate resistance prediction compare to the model test at even keel. However, the trend for CFD result at speed below 15.5 knot are not similar with model test. This is due the fact that the bulb effect is neglected for CFD calculation. As for tanker ship, zonal method CFD mostly failed to give similar propulsive power trend with experimental result. At 30 kilo Ton (kT) loading condition, however, the trend is similar on both zonal CFD and model test result. Global RANS was only succeeded to run at speed of 8, 9 and 14 knots