Experimental and computational study of operation of an amphibious craft in calm water

Abstract

The hydrodynamic characteristics of a waterjet-propelled amphibious craft traveling in displacement and planing modes are studied via full-scale experiments and numerical simulations in three ways. First, variations of pitch, resistance, and vertical rise for speeds from 2 to 18 knots are investigated. As speed is incrementally increased, pitch and resistance increase geometrically before maximizing in the transition region. In this region, the computations underpredict pitch, yet resistance matches the steady-state thrust measurements well. Second, maneuverability in displacement mode at 4 knots is investigated with a zigzag maneuver. Time variations of heading, pitch, yaw rate, roll, and roll rate predicted by computational fluid dynamics (CFD) for the zigzag maneuver are in good agreement with the experimental results. Third, the dynamic transition from displacement to planing mode is investigated by abruptly increasing the thrust beyond the craft's peak resistance. Beyond the resistance maximum, the vehicle experiences a sharp increase in speed and drop in pitch angle. Experiment and simulation conclude similarly with an abrupt cut to propulsion, resulting in a quick deceleration, which is overcome by its own wake. Simulated kinematics of the deceleration are remarkably accurate, suggesting valid computations of the transient drag, wake generation, and vehicle response to waves.