Efficient Time-Domain Simulation of Side-By-Side Moored Vessels Advancing in Waves

Abstract

Evaluation of hydrodynamic performance of two vessels in close proximity that are either stationary or advancing in waves is of paramount importance for many offshore and naval engineering applications. Hydrodynamic interactions between the vessels combined with nonlinear mechanical interactions due to mooring and fendering systems make the problem more complicated. An efficient time-domain method is presented for evaluating the seakeeping and maneuvering performance of proximate vessels advancing with forward speed. The method computes the 6 degree-of-freedom motions of a pair of hydrodynamically interacting vessels subject to wind, waves, currents and maneuvering effects at zero and nonzero speeds in regular or random seaways. Model tests conducted to validate the method are described and results presented. The validation efforts conducted so far have yielded satisfactory comparisons, thereby reinforcing the confidence in the method and its applicability to such problems. The method has been used to predict safe operational limits of two vessels in skin-to-skin operations conducted by the US Navy. A similar analysis is presented herein for a different pair of vessels. Since it is based on time domain simulation, this method also allows the inclusion of non-linear effects due to mooring lines, fenders and effects of viscous roll damping, which is not possible with two-body hydrodynamic interaction solutions in frequency-domain. It is concluded that this method provides an efficient tool to predict the performance of hydrodynamically interacting vessels that are stationary or moving with forward speed. To date, it has proven very useful in the early stages of the design/concept development process in which many configurations are evaluated.