ABSTRACT

There are several methods for ship resistance calculations. Computational Fluid Dynamics (CFD) applications, other numerical methods, experimental and statistical methods are the mainly used methods. Resistance are calculated at different velocities and ship operation conditions to get an optimum hydrodynamic form. Therefore, the ship resistance calculation method should be suitable for a systematic and repetitive application. Due to these reasons, the CFD method is used widely for ship resistance calculations. It has been possible to calculate total resistance for ships with the developing computer technologies. However, calculation of total ship resistance with CFD still requires high calculation capacity and long calculation times. Generally, ship resistance calculations with CFD are performed at model scale. Model resistance is then extrapolated to full ship scale. International Towing Tank Conference (ITTC) 1957, Hughes-Prohaska and ITTC 1978 are the most common extrapolation techniques.

Telfer’s GEOSIM (GEOmetrically SIMilar) method developed in the distant past is another technique for ship resistance problems. Total resistance coefficients of hulls are computed at different scale ratios. These models have geometric and kinematic (Froude) similarities. Non-dimensional resistance coefficients are then plotted against Reynolds numbers. After that the ship resistance at full scale is computed by a simple extrapolation technique. Unlike other methods, in the Telfer method, total ship resistance is not separated into its components. It is known that the Telfer method is a very successful method to predict the ship resistance. However, this method is expensive in experimental studies as it requires different scaled models to be produced and multiple model tests. In this study, resistance values have been calculated for a benchmark hull geometry, Duisburg Test Case (DTC) which is commonly used in computational ship hydrodynamics studies. In the beginning of CFD analyses, mesh independence studies were conducted for one single scale and the output was applied to the other scales in proportion with the model lenghts. It is aimed to calculate total ship resistance accurately without seperating it to its components. CFD computations are made on six different scaled models and total resistance coefficients are obtained for these models. In “Tefler Method” model tests are replaced by CFD analyses. Then the Tefler method is modified to enhance the accuracy.