Urans and des simulations of static and dynamic maneuvering for surface combatant

Unsteady Reynolds Averaged Navier Stokes (URANS) simulation and Detached Eddy Simulation (DES) are performed for a surface combatant Model 5415 bare hull in static and dynamic planar motion mechanism (PMM) tests. The objective of this research is to investigate the capability of the general purpose URANS/DES research code which has been developed by IIHR ship-hydrodynamic group at the University of Iowa to the computational fluid dynamics (CFD) based maneuvering prediction method. This study is complementary to IIHR towing tank PMM experiment. In this research, the model is subjected to static drift, steady turn, pure sway, pure yaw and combined yaw and drift motions at Fr=0.28. The results are analyzed in view of: (1) the verification for iterative, grid, and time-step convergence along with assessment of overall numerical uncertainty; (2) detailed validation studies for static and dynamic PMM simulations, including force and moment coefficients, hydrodynamic derivatives, and reconstructions, and; (3) local flow analysis for static and dynamic PMM simulations, including wave pattern, boundary layer and vortices, validation with the PIV measurement results of velocity and turbulence at 2D cross sections, and Fourier series reconstructions. Results from each analysis show: (1) Forces and moment in both static drift and pure yaw cases show stronger grid dependency than time step, and the locally refined grid up to 250M significantly decreases the grid uncertainty; (2) Current URANS simulations can accurately predict most of acceleration and linear derivatives with relatively coarse grid, while the DES simulation with finer grid will be effective for better predictions in non-linear derivatives; (3) Single-run method to calculate linear hydrodynamic derivatives from the results of dynamic PMM tests is applicable not only for Model 5415 bare hull but also for appended hull, tanker and container ship; (4) Current URANS/DES simulations can alternate pure sway experiment, while more diagnostics for the modeling, numerical methods and results will be required to determine if it can alternate pure yaw and combined yaw and drift experiments; and (5) Current URANS/DES simulations can predict the general trend of steady and unsteady features of local flow quantities by static and dynamic PMM tests, but again, the DES with finer grid will provide better estimation especially near the vortex core vicinity. Overall, the current study shows that current URANS/DES simulation for static and dynamic PMM tests has fundamental capability to estimate the ship maneuverability, and will be the effective tool for a CFD based maneuvering prediction method.