The wave action due to a sudden impulse in a body of water was studied in a wave basin with beach in the laboratory. Waves were impulsively generated in the 90 ft. tank of water, 3 ft. deep, by the impact or sudden withdrawal of a paraboloidal plunger 14 ft. in diameter. The waves had a dominant height of 2 inches and period of 3 seconds, respectively, at a distance of 50 ft. from the plunger. Such waves are scale representations of those generated by sudden impulses in the ocean, such as an underwater nuclear explosion, a sudden change in the ocean bed due to earthquakes, or the impact of a land slide. The waves produced by a downward impulse, or by an underwater explosion, form a dispersive system: whose properties are not constant as in a uniform progressive wave train. Wave periodicities, celerities and wave lengths increase with time of travel and wave heights decrease with travel distance. Theory has already been developed to predict the wave properties at a given travel time and distance for given source energy, displacement and travel path depth profile (Jordaan 1965). Measurements agree fairly well with predictions.
This paper is a summary of the results of investigations of the drop in potential and boundary resistance in unsteady motion for cases of surface resistance caused by boundary shear stresses and cases of form-type resistance associated with the high shear and generation and diffusion of turbulence accompanying jet formation. These cases were obtained using uniform diameter conduits and orifices in conduits. From tests in the MIT unsteady flow water tunnel, the effects of accelerated and decelerated flows were studied. In the case of flow through a uniform tube, it was found that the boundary resistance at any instant during accelerated motion was slightly greater than the equivalent steady-state case while, for decelerated motion, it was slightly less. In the case of flow through orifices, it was found that the combined resistance of the orifice and the conduit was less during accelerated motion and more during decelerated motion than for the equivalent steady-state cases.
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