The Office of Naval Research’s (ONR) Surface Ship Hydrodynamics Program has contributed to ship design and performance in many respects, particularly in measurement techniques at model and full scale, theoretical descriptions of ship motion and fluid mechanics, and advanced computational techniques which continually have pushed the capabilities of the best computers. Prediction of ship motion characteristics in extreme conditions is fundamentally challenging in that it deals with highly nonlinear processes and involves the statistics of rare events. Though the computational methods of today are extremely advanced, the demand on resources is so phenomenal that there is a constant trade-off between sophistication and turnaround times.
Likewise, the understanding of the air entrainment and bubble wake processes are so complex that even a ranking of sources is still uncertain and may vary from ship to ship. Great strides have been achieved in prediction of wave-breaking occurrence and of the overall fl owfi eld around the ship. However, the details of air entrainment still require extensive research to permit the formulation of models to include in prediction methods.
Specifi c objectives of the ONR program include proper mathematical representation of waves and wave-ship interaction in extreme conditions, the physics of air entrainment by breaking waves, the turbulent contact line, propulsion, and transom fl ow, the submergence, transport, and evolution of air and bubbles in steady and unsteady conditions, and the processes determining the size spectrum of bubbles during wake formation. Important factors in the bubble wake include seawater effects such as salinity and surfactants, incident waves, and ship motion. Ship motion prediction is focused on steep nonlinear waves and the nonlinear response of the ship, including viscous effects such as roll damping. Future directions will include the effects of damage and flooding.
Advances in the fi eld of ship hydrodynamics will have broad impacts in ship design and operation. Accurate prediction of motions and the resulting loads will assist structural analyses during design and provide either automatic control or operator guidance in extreme sea conditions. Prediction of the bubble wake may permit modifi cations in design or operation to minimize ship vulnerability. In both topics advanced computational techniques will shorten design cycles and broaden the space of design options with higher confi dence in the results.