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The nonlinear viscous-flow problem associated with the heaving motion of a two-dimensional floating cylinder is considered. It is formulated as an initial-boundary-value problem in primitive variables and solved using a finite-difference method based on boundary-fitted coordinates. A fractional-step procedure is used to advance the solution in time. As a case study, results are obtained for a rectangular cylinder oscillating at a Reynolds number of 103 . The nonlinear viscous forces are compared with those of linear potential theory. An assessment on the importance of viscous and nonlinear effects is made. The solution technique is sufficiently robust that extensions to consider other single and coupled modes of motion are possible.

Sea-keeping characteristics of a wave-adaptive modular catamaran, developed by Marine Advanced Research Inc., is studied using at-sea experiments and dynamic modeling. The vehicle is based on the Proteus design and is supported by two inflatable pontoons with each pontoon attached to a center payload tray using an independent suspension system connected in such a way that the demi-hulls perform somewhat independent motions through a wave field. The suspension system is designed to isolate the center payload tray from the motions induced by waves incident on the demi-hulls. The vehicle is propelled by two water jets and is capable of achieving speeds of 8–15 knots. Accelerometers have been mounted on the pontoons and the center payload tray of the vehicle and field tests in the open ocean have been carried out to study sea-keeping properties of the vehicle. Heave and surge motions for the cases of following seas, beam seas and head seas have been recorded. In each case the center payload tray is found to experience attenuated heave accelerations compared with the two pontoon hulls. The reductions in surge and sway motion are, however, not evident. The associated spectra suggest that heaving motion of the center payload tray over a range of frequencies is attenuated by the suspension system. No attenuation is apparent in the surge and sway motions. The WAM-V dynamics is modeled as a three-body problem with the pontoons corresponding to bodies 1 and 2, and the central tray to body 3. Results of the analysis are compared with the sea trials.