Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019
expensive. Kinematic similarities can also be violated during tests due to the effects of tank side walls particularly for large models and occurrence of much laminar flow near bow section of small models. Estimation of resistance from model scale to full scale can lead to inaccuracies, especially in high Reynolds numbers. Due to such major disadvantages, this method has not been preferred much to determine the total resistance of ships at full scale. But now CFD and numerical towing tank applications have been widely used. The solution to ship resistance problem has been facilitated using developed processing capability and CFD applications for both model families and ships at full scale. Many features of a hull can be investigated in processing and post-processing stages both numerically and visually by CFD methods. Here original Telfer’s GEOSIM method has been revisited by using CFD applications
CFD method has widely been used to solve the ship hydrodynamic problems. Shen et al. (2015) have simulated towed tests of KCS, open water tests of the KP505 propeller, self-propulsion and zig-zag manoeuvres of KCS model to validate the dynamic overset grid technique. Gaggero et al. (2015) have showed that the hydrodynamic properties of KCS hull could successfully be investigated with OpenFOAM RANS solver.Ozdemir et al. (2016) have investigated the capability of a CFD code on KCS hull. Numerical results have been compared with the available experiment data. In the study of De Luca et al. (2016), a comprehensive V&V study was conducted to assess the reliability of URANS simulations of a planing hull. RANS based CFD approach was applied for wave resistance problem of ships in Kinaci et al. (2016). They also examined the dependency of form factor to Reynolds number. Self-propulsion points of KCS hull have been obtained with the methods based on CFD approach in Kinaci et al., (2018). They have also proposed a simple method for predicting self-propulsion points of marine vehicles using some empirical relations.Gokce et al. (2018) have predicted hydrodynamic characteristics of Japan Bulk Carrier (JBC) using RANS method. Numerical results have been compared with empirical relations recommended by International Maritime Organization (IMO). The numerical results have been found more robust than IMO recommendations. Sezen et al. (2018) have examined the hydrodynamic properties of a submerged body in a wide velocity range by RANS approach.
In the past GEOSIM series have generally been used to
study the scale effects on the form factor, e.g., Garcı́a- Gómez (2000); Lin and Kouh (2015); Srinakaew (2017). For example, Kouh et al. (2009) have numerically investigated the scale effect on form factor. Four surface ship and two sub-bodies have been simulated with double- model flow in a wide range of Re numbers. The difference between these studies and this study is that only one scale of each hull was performed with different Re numbers. In present study computations have been carried out at different scale ratios. Flow interference phenomena between catamaran hulls has also been examined
numerically with GEOSIM approach in Broglia et al. (2011). In contrast to these studies, GEOSIMmodel series have been applied to estimate the total resistance of full scale ships in the present study.
CFD methods can also be used to solve the complex flow problem around hull forms not only at model-scale but also at full scale. In study of Castro et al. (2011) resistance and self-propulsion simulations of the KCS hull at full scale have been carried out numerically. The coefficients obtained from CFD have been compared and discussed with the results from ITTC extrapolation procedures. Tezdogan et al. (2015) have predicted ship motions and added resistance of a full scale KCS hull with fully nonlinear unsteady RANS method. The results have been validated with available experimental data and also compared with those of potential flow theory. Park et al. (2015) have proposed a new method for the propulsive performance prediction at full scale, including the effect of an energy saving device (ESD). Free surface effect has not taken into account in full scale CFD analysis. Lin and Kouh (2015) have performed a numerical resistance test, open water performance and self-propulsion tests at different scales of KCS hull without considering free water surface effects. As a result of the study, the scale effect on thrust deduction has been discussed and compared to the conventional standard ITTC procedure. Haase et al. (2016) has proposed a novel CFD-based approach to predict the resistance at full scale. For both model and full scale CFD simulations, model tests and sea trials have been used for an agreement of resistance with established model-ship correlation lines and surface roughness effects. In another study of Tezdogan et al. (2016), the seakeeping behaviour of a full scale large tanker and its heave and pitch responses to head waves hull have been investigated at various water depths. Numerical results have been reported to be consistent with the experimental results and the results from 3D potential theory. In the paper of Jasak et al. (2018), full scale CFD self-propulsion has been compared with sea trials for two types of ships: a general cargo and a car carrier. The results obtained from full scale open water propeller tests have been used as an input in self-propulsion with the actuator disc model. Song et al. (2019) have examined the effect of barnacle fouling on the resistance and wake characteristics of full scale KCS hull. The roughness function has been validated with model-scale flat plate simulation then this approach has been employed in full scale flat plate simulation and full scale 3D KCS hull simulations.
In the present study, the total resistance of a full scale ship has been predicted using Telfer’s GEOSIM method (Telfer, 1927) based on CFD approach. The model tests of the KCS hull at 60.75 scale ratio were also conducted in the Ata Nutku Ship Model Testing Laboratory of Istanbul Technical University. Numerical analysis of KCS hull at three different model scales and full scale have been carried out by the fully nonlinear unsteady RANS method. In order to determine the grid independence of the numerical model, a spatial convergence study has been
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©2019: The Royal Institution of Naval Architects
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