1. Tokyo 2015 A Workshop on CFD in Ship Hydrodynamics URANS Simulation of Surface Combatant using CFDShip-Iowa V.4 S. Bhushan and F. Stern IIHR-Hydroscience & Engineering, The University of Iowa, Iowa City, IA 52246, USA. MODELING Governing Equation: Single-phase Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are solved in relative inertial coordinates (Carrica et al. 2007). Turbulence Modeling: Isotropic two equation blended k-ω/k-  model (Menter 1994 ). Interface Modeling: Free-surface is obtained by solving level-set equation. 6DOF: Rigid body linear transformation/rotation about center of gravity. A dynamic overset grid approach is used to allow relative motions between the grids. Propeller Model: Axisymmetric body force propeller model. Numerical Method Discretization: Finite difference method for body fitted curvilinear grids. 2nd-order backward Euler predictor-corrector scheme is used for time stepping. Convection term is discretized using a 2nd-order upwind scheme and diffusion term using 2nd- order central difference scheme. Velocity-pressure coupling : Mass conservation is satisfied using a PISO scheme. Dynamic overset grid: SUGGAR is used to obtain grid interpolation coefficients. Iterative solvers: ADI line solver is used for solving equations implicitly, PETSc toolkit is used for solving pressure Poisson equation. High Performance Computing Message Passing Interface (MPI) based domain decomposition is used, where each decomposed block is mapped to a single processor. Computational Expenses: 4.04M grid is solved on 32 processors for 3L/U 0. Simulation took 42hours of clock time and 1344 hours of CPU time. Platform: NAVO’s IBM P5 Babbage which consist of 16 CPUs/node with 32GB memory per node, processor clock speed of 1.9GHz, and bandwidth of 7.4Gbps. Grids, Domains, Boundary and Flow Conditions Grids: Three systematically refined grids fine (4.04M), medium (1.4M) and coarse (0.61M) obtained a using grid refinement ratio (r G ) of  2. Averaged y + =1.1. Domain: Half domain simulation using symmetry at Y=0. Domain size in [X,Y,Z] is [-2.0-23.0L, 0-2.0L, -2.0-1.0L]. Boundary Conditions: Hull has no-slip, X- min is uniform velocity U 0, X-max is convective, symmetry is used for Y=0, Y- max and Z-max use inlet velocities and zero-gradient for pressure, Z-min is a slip boundary. Flow Conditions: FX , Re = 5.13×10 6, Fr = 0.28,  = -1.92×10 -3,  = -0.136 . VERIFICATION AND VALIDATION Verification study is performed to obtain grid convergence uncertainties (U G ) following the quantitative methodology and procedures proposed by Stern et al. (2006). U I /  12 =0.24,0.4 and 0.87 for c T, c F and c P, respectively. Monotonic convergence is obtained for the resistance coefficients. p G /p G,th is close to 1 for c T but around 2 for c F and c P. U G =2.2%D for c T and <1%D for c F and c P. E for c T on fine grid = 3.07%D < U V =3.6%D. Thus c T prediction is validated. U G estimates for c P could be contaminated by U I. Table: V&V study for FX  5415 resistance prediction, Re = 1.19×10 7, Fr = 0.28,  = -1.92x10 -3,  = -0.136 . V4 predicts the sonar dome rotating vortex and its interaction with boundary layer fairly well when compared with the EFD data. However, the sonar dome vortex is over predicted at development and the after body shoulder vortex is not resolved well suggesting rapid dissipation of the vortex. At the nominal wake plane the boundary layer is thicker at center plane compared to the EFD data and the bulge is underpredicted due to weak vortex strength. The TKE and stress contours compare well with EFD qualitatively but not quantitatively. References Carrica, P. M., Wilson, R. V., Noack, R. and Stern, F. 2007, “Ship motions using single-phase level set with dynamic overset grids,” Computers and Fluids, 36(9), 1415-1433. Menter, F.R. 1994, “Two Equation Eddy Viscosity Turbulence Models for Engineering Applications,” AIAA Journal, 32(8), 1598-1605. Stern, F., Wilson, R. and Shao, J., 2006, “Quantitative approach to V&V of CFD simulations and certification of CFD codes,” International Journal of Numerical Methods in Fluids, 50, 1335-1355. Acknowledgment This research was sponsored by the Office of Naval Research administered by Dr. Patrick Purtell under grant number N00014-01-1-0073 and N00014-06-1-0420. Figure: Simulation domain, grid topology and boundary conditions. Figure: Boundary layer profile (left panel), TKE distribution (middle panel) and shear stress distribution (right panel) on the nominal wake plane (x/L=0.935) are compared with EFD data. Figure: Boundary layer and wake profile at x/L=0.6 is compared with EFD data. Figure: Wave elevation contour is compared with EFD data. SUBMISSION EXPLANATION Test cases: Case 3.1a and 3.1b Name of the Code: CFDShip-Iowa V.4 Institution: IIHR, The University of Iowa