UNSTEADY RANS SIMULATIONS FOR A CATAMARAN ADVANCING IN REGULAR WAVES

The response of a catamaran advancing in regular head waves is analyzed numerically with the Unsteady RANS Code CFDShip-Iowa V.4. The model advancing in regular head waves has been studied for Fn=0.45, Fn=0.6 and Fn =0.75. For each speed, a range of wavelenghts going from λ/Lpp =0.9 to λ/Lpp=2 has been considered, to evaluate the effects of wavelenghts on maximum response. Simulations have been conducted for a wave steepness Ak=0.025 for which experimental results are available. Effects of wave steepness have been investigated for selected conditions, although experimental data is lacking for validation. To determine the added resistance in waves, the catamaran has been studied in calm water too, for a speed range varying from Fn=0.3 to Fn=0.75 and resistance, sinkage and trim have been evaluated. For heave motion, the maximum response is registered in resonance conditions and for the highest speed (Fn=0.75), while exciting loads of incoming wave seem to have effects on maximum response only for wavelenghts higher than λ/Lpp=1.1, depending on speed. For Fn=0.75 the effects of wave steepness have been evaluated too, and results for Ak=0.025, Ak=0.05 and Ak=0.1 have been compared. Results show that for high wavelenghts (λ /Lpp > 1.9) the catamaran exhibits a linear behavior while it’s non linear for lower wavelenghts. The added resistance results were expressed in terms of the added resistance operator δCT/A 2 . Results show that the maximum value of added resistance is for Fn 0.45 and the dependence on wave steepness is also evaluated and consistent with the non linear behavior of heave and pitch.