The commercial CFD software STAR-CCM+ is applied as a RANS solver for comparison with potential flow methods in the calculation of vertical plane radiation and diffraction problems.  A two-dimensional rectangular cylinder oscillating in an unbounded fluid is first considered, and the added mass result shown to agree well with the analytical potential flow solution.  Hydrodynamic coefficients are then determined for the cylinder oscillating in heave and sway about a calm free surface.  Predicted values are observed to coincide with available experimental and linear potential flow results for most amplitudes and frequencies of oscillation examined.   A three-dimensional radiation problem is then studied in which 1-DoF heave and pitch motions are prescribed to the ONR Tumblehome hullform in calm water at zero forward speed and Fn 0.3.  Combinations of amplitude and frequency of oscillation ranging from small to large are considered.  Results are compared with several potential flow codes which utilize varying degrees of linearization.  Differences in the force and moment results are attributed to particular code characteristics, and overall good agreement is demonstrated between RANS and potential flow codes which employ a nonlinear formulation.  The ONR Tumblehome is next held static in incident head waves of small and large steepness and zero forward speed or Fn 0.3.  Force and moment time histories of the periodic response are compared with the same set of potential flow codes used in the radiation problem.  Agreement between potential flow and RANS is reasonable in the small wave steepness case.  For large wave steepness, the nonlinear wave response is seen to be important and the RANS solution does not generally agree well with potential flow results. / Master of Science

Calm water towing tank experiments consisting of resistance tests and static and dynamic planar motion mechanism (PMM) tests are performed for a surface combatant with primary focus on the effects of hurricane scale headwinds. The experiments are designed to gain a better understanding of the physics of ship response to wind and to provide a validation dataset for an unsteady Reynolds-averaged Navier Stokes (RANS)-based computational fluid dynamics (CFD) code used for computing both air and water flow around a ship. Hurricane scale wind speeds are chosen to maximize the measurable effect of wind on ship forces and motions for a more definitive analysis and comparison with CFD. The geometry is the 1/48.9 scale fully appended ONR Tumblehome model 5613, which has length L = 3.147 m and is equipped with a superstructure. Tests are performed in a 3.048 × 3.048 × 100 m towing tank with wind generated by a custom built wind carriage towed ahead of the ship model. Air-stream velocity measurements indicate a maximum relative wind speed magnitude of 9.38 m/s with 6 - 7% uniformity and RMS values of approximately 4.5%. The effects of three wind speeds on static and dynamic forces, moment, and motions are analyzed. Results show that wind contributes significantly to surge force (approximately 46% at Fr = 0.2). Resistance data shows agreement with CFD computations with errors averaging approximately 4%. The drag coefficient above water is approximately 0.3 and generally decreases with increasing ship speed. Sway force and yaw moment are largely affected when the ship experiences oblique orientation to the flow. Forces and moment exhibit quadratic scaling with wind speed. Roll is the most sensitive motion to wind and is counteracted by it up to 1.8° for PMM test conditions. In addition, harmonic amplitudes of forces and moment data from dynamic tests are used to determine hydrodynamic derivatives for all three wind conditions following a mathematical model. The effect of wind on hydrodynamic derivatives is significant with changes on the order of 10 - 100%.