Experimental and numerical study of the added resistance and seakeeping performance of a new unmanned survey catamaran

Experimental and numerical methods were employed to investigate the added resistance and seakeeping performance of an innovative unmanned catamaran for offshore surveying. Model experiments validated numerical results from viscous flow computational fluid dynamics (CFD) modeling using the unsteady Reynolds-averaged Navier-Stokes (URANS) equations and the potential flow method. URANS modeling precisely predicted the catamaran's performance in regular waves, and the potential flow method offered effective short-term predictions in irregular waves. Simulations were performed at three velocities (4, 6, and 8 knots). The results highlight the fundamental relationships between added resistance and motion responses with changing wave conditions. The extreme motion responses generated by typical actual sea conditions are summarized. The added resistance and motion responses are greatest when the wavelength is slightly longer than the length of the catamaran and the encounter frequency, f(e), is similar to 1.2. The optimal velocity of the catamaran is 6 knots. The seakeeping performance of the catamaran was assessed using existing indicators for manned vessels. Compared with manned vessels, unmanned survey vessels are more tolerant of first-order motion response but require stricter limitations on second-order accelerations in each degree of freedom.