ABSTRACT

In this study, the analysis of 2DOF (2 Degree Of Freedom) motion and added resistance of a ship in regular head waves is carried out using RANS (Reynolds Averaged Navier-Stokes) approach. In order to improve the accuracy for large amplitude motions, the dynamic overset scheme is adopted. SUGGAR++ which is the dynamic overset scheme library is applied to WAVIS2, the in-house RANS code of KRISO (Korea Research Institute of Ships and Ocean Engineering). The grid convergence test is carried out using the present scheme before the analysis. The target hull form is KRISO VLCC tanker (KVLCC2) and 13 wave length conditions are applied. The added resistance coefficients, heave and pitch motion RAO computed by using Suggar++ are compared with those from the experiment. The present scheme shows the improved results comparing with the non-inertial reference frame based solver. It is confirmed that the dynamic overset scheme has the advantage for the large amplitude motion cases.

INTRODUCTION

With the introduction of the EEDI (Energy Efficiency Design Index) regulation of the IMO (International Maritime Organization) in 2015, there has been a steady increase in interest of the added resistance in waves in the industrial and research field. The added resistance in waves is related to the weather correction factor of EEDI index and is a component that affects the actual operating efficiency of the ship as a resistance component added by the waves when the vessel is operating at sea.

The method for predicting the additional resistance in waves of a ship can be divided into an experimental method and a numerical analysis method. As the experimental studies, Storm-Tejsen et al. (1973) introduced an added resistance test for Series 60 hull form and then Journee (1992) carried out the Wigley hull test. In order to see the effect of the devices for reducing the added resistance, Hirota et al. (2004) and Kuroda et al. (2012) tested Ax-bow and Leadge-bow for slow speed ships and STEP for fast ships, respectively. Recently, Valanto and Hong (2015) published the test results for HSVA hull model and Park et al. (2015) introduced the uncertainty analysis for added resistance experiment of KVLCC2 ship using ITTC procedure. Numerical analysis can be divided into two approaches, one is potential theory based method and the other is CFD (Computational Fluid Dynamics) method using Navier-Stokes equations. Traditionally, potential based methods have been widely used to predict the effects of radiation wave. Recently, due to rapid development of computational techniques, there are many attempts to approach for predicting added resistance using CFD. As potential based approaches, Salvesen (1978) and Faltinsen et al. (1980) introduced the near-field method and Maruo (1960) and Gerritsma and Beukelman (1972) suggested the far-field method. Recently, Joncquez et al. (2008) computed the added resistance of Wigley, Series 60, and a bulk carrier using BEM (Boundary Element Method) and Kim and Kim (2011) proposed the appropriate criterion of using a time-domain Rankine panel method for the prediction of added resistance in irregular waves. Seo et al. (2013, 2014) conducted the comparative study of different numerical schemes and formulations for computing added resistance. As CFD approaches, Orihara and Miyata (2003) calculated the added resistance of SR108 container ship and mid speed tanker using WISDAM-X based on RANS approach. Carrica et al. (2007) and Castiglione et al. (2009) carried out 6DOF motion analysis of DTMB5415 and computed added resistance of DELFT 372 catamaran using the overset grid, respectively. Simonsen et al. (2013) introduced motion analysis of KCS in head sea condition and Seo and Park (2017) used OpenFOAM for motion analysis of KCS in regular head waves.

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