Trans RINA, Vol 161, Part A4, Intl J Maritime Eng, Oct-Dec 2019


hull in this towing tank has been estimated as ± 1.16% according to ITTC (2014b) method for Fr=0.26 (Delen and Bal, 2015b). In this study, the experimental results have been used only for validation. A profile view of KCS at the Fr=0.26 has been shown in Figure 2.


(2017). Computational domain and boundary conditions have been shown in Figure 3.


5.2 GRID STRUCTURE


Figure 2. A profile view ofModel 1 at Fr = 0.26. 5.


NUMERICAL SETUP 5.1


COMPUTATIONAL DOMAIN AND BOUNDARY CONDITIONS


Dimensions of computational domain (-1≤ x/LPP ≤3, 0≤ y/LPP ≤2, -1.5≤ z/LPP ≤0.5) have been selected to take into account ITTC (2011b) recommendations and to avoid any influence on the wave pattern. The Cartesian coordinate system was adopted in the CFD analysis. The origin of coordinate system is at the point where fore perpendicular intersects the waterline. The positive x-, y-, z- axes have been defined as in the stream-wise, starboard and upward directions, respectively.


In order to reduce the


computational time, half of the hull (only starboard side) has been used in the analysis. The centreline of KCS hull has been defined as the symmetry plane. The upstream and surrounding boundaries have been defined as velocity inlet to impose Dirichlet type of boundary condition. This boundary condition is very suitable for the incompressible flows, in which the velocity profile is known at inlet boundary. The downstream boundary has been defined as pressure outlet (gradient normal to the boundary of velocity) by Neumann boundary condition. No-slip kinematic boundary condition has been adopted on the hull surface. Detailed information on the boundary conditions can be found in the user guide of CD-adapco


Computational domain has been created by the overset mesh technique due to the large amplitude motions of form (especially in full scale condition). There should be a good overlap between the background and the overset grids in order to represent the flow accurately around the hull form. The dimensions of overset domain have been taken as -0.12≤ x/LPP ≤1.12, 0≤ y/LPP ≤0.12 and -0.12≤ z/LPP ≤0.12. The computational domains have been divided into unstructured hexahedral cells. The mesh structure has been refined in terms of cell size, especially on free surface and in the wake region. The total numbers of mesh forModel 1,Model 2,Model 3 and full scale ship are 1.89, 2.41, 2.52, 11.5 million, respectively. Mesh structure along the centreline of KCS can be seen for Model 1 in Figure 4.


Figure 4. Grid structure of KCS (Model 1). 5.3


SOLUTION STRATEGY


The governing equations have been discretized using a cell based finite volume method (FVM). SIMPLE (Semi- Implicit Method for Pressure-Linked Equations) algorithm which allows to couple the Navier-Stokes equations with an iterative procedure has been used to solve the pressure field. The flow around the hulls has been considered fully turbulent, 3-D and multiphase. To simulate the flow around the hull, the k-ε turbulence model has been selected. Quérard et al. (2008) reported that the k-ε model is more economical in terms of CPU execution time than k-ω turbulence model.


Figure 3. Profile and side views of the computational domain with boundary conditions.


©2019: The Royal Institution of Naval Architects


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