Application of CFD to Study Performance of Hydrofoil-Based Ship-Stabilization Systems

Computational Fluid Dynamics is used for simulating the flow over an oscillating hydrofoil found in a typical active-fin ship stabilization system. The hydrofoils oscillate through large angles of attack well above the static stall angle to generate large lift forces. Lift forces are calculated on the hydrofoil by using a simple sinusoidal motion at mean frequency of fin oscillation. The lift data is used in a linear system model created to simulate the active-fin ship-stabilization system. A Proportional Integral Derivative (PID) control system has also been developed for the purpose of controlling the fin motion. The simulation provides the typical motion experienced by a hydrofoil used in a ship stabilization system. This motion is fed back to a CFD solver to understand the effect of non-sinusoidal oscillation on Lift, Drag and Moment of the hydrofoil. The aerodynamics of the non-sinusoidally oscillating hydrofoil is analyzed so as to find the effect of pitch rate of the hydrofoil on the lift forces and hence on the performance of the ship stabilizer.