Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
already a form factor correction (ITTC, 2011c). All estimated results (by Telfer and ITTC methods) have been compared with those of CFD method at full scale as shown in the Table 5. Relative difference (between the resistance of Telfer’s GEOSIM method (TGM) and that of CFD (∆% = 100 × |− −−|/−) is less than that of ITTC 1978 method and CFD (∆% = 100 × |− − −|/−). This is very clear in Table 5. The numerical resistance values and extrapolated results by both Telfer’s GEOSIM method and ITTC method have been shown in the Figure 10. Resistance value at full scale by Telfer’s GEOSIM method is closer to that by CFD than resistance value calculated by ITTC 1978 method. This can be due to not decomposition of total resistance into components by Telfer’s method.
represent the slope of the curve much better as shown in the total resistance coefficient curve (Figure 11).
Figure 11. Comparison of nominal wake fractions by different method
8. CONCLUSION Figure 10. Comparison of total resistance coefficients.
Telfer’s GEOIM method has also been extended to the prediction of wake fraction of ship at full scale. Coefficients (a, b and x) have been calculated as -93.291, 0.885 and 3.191, respectively, for the full scale nominal wake fraction. Wake scaling has been successfully represented by the Telfer’s GEOSIM method as given in Table 5. Relative difference between the wake fraction by Telfer’s GEOSIM method (TGM) and that of CFD (∆%(1 −) = 100 × |(1 − ) − (1− )|/ (1− )) has been found to be less than
1%.Wang et al. (2015) had previously proposed a method with a relationship between the nominal wake and Re number similar to this method. However, in this study, the exponential force of log(Re) has also been calculated to
Telfer’s GEOSIM Method
2.306 % Δ(1-wn)
0.816 -
0.53% 0.811
0.53%
In this study GEOSIM method of Telfer has been applied to compute the ship total resistance coefficient and nominal wake fraction at full scale by CFD analysis. KCS hull has been selected to validate the results. Numerical results of models at three scale ratios have been compared and validated with those of experimental data. Full scale resistance analysis of KCS hull has also been performed numerically. The extrapolated full scale results (GEOSIM method and ITTC 1978 method) have been compared with those of CFD analyses. Resistance values extrapolated by ITTC 1978 method have been found about 5% smaller than that of CFD at full scale. This difference is less than 1% by the Telfer’s method. It has been found that Telfer’s GEOSIM method in a wide range of Re numbers can be successfully used with the help of the numerical models at three scales. There is no need to decompose the resistance components and to solve ship flow problem at full scale which requires too much computational time.
This method has also been extended to the estimation of nominal wake fraction in a way similar to total resistance coefficient. The estimated nominal wake value has also been found in a good agreement with that of CFD analyses.
Table 5. Comparison of full scale resistance methods for KCS at Fr = 0.26. CFD Method 2.294
CTS*103 %ΔCTS 1-wn
-
λ=60.75 2.177
5.08%
ITTC 1978 Method λ=37.89 2.183
4.86%
λ=31.6 2.186
4.70%
©2019: The Royal Institution of Naval Architects
A-475
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