A basic mechanism is proposed to explain the growth of finite amplitude water waves due to the effect of normal stresses. The proposed mechanism can probably be applied to the whole range of wave's growth, starting from a small amplitude wave up to the case of a limiting and breaking wave condition. The transfer of energy from air flow to the water wave is explained by the existance of a circulation flow pattern above the water surface, which is responsable for a phase-lag of the normal stress distribution in relation to the wave's profile. Such a circulation flow pattern extends throughout the whole wave length and it is quite different from the classical concept of flow separation, as postulated by Jeffrey's. The difference becomes as a result of considering a different boundary condition at the interface. Experiments performed on wavy models with moving boundary conditions, for small amlitude waves and finite amplitude waves showed that the normal stress distribution is similar in both cases, and displays a noticible phase-lag with respect to the wave's profile. It was observed that for both cases a circulating flow pattern was present above the water surface, which indicated some relation between the flow vorticity above the wave and the normal stress distribution. To prove the role of circulation in the energy transfer mechanism, a model was built with water and mercury as working fluids. In this model the interface was initially non disturbed, when both fluids move in opposite directions. However, when a forced circulation was applied by means of a variable speed rotor located above the interface, a wave would form. The wave would be inicially of small amplitude, but with an increase of circulation would become of finite amplitude, then reach the angular crest condition and finally would reproduce the breaking condition at the crest. The obtained experimental results proved the importance of the circulation flow pattern present above the wave surface, and suggest that a mathematical model could be formulated based on vorticity analysis, which would be able to provide an explanation for the energy transfer mechanism due to normal stresses at all stages of wave's growth.
Experimental data on pressure distribution over a sinu^ soidal wavy boundary with a fixed and a moving condition, mea_ sured in a water tunnel, are presented for a number of flow - velocities. The model with the moving boundary condition is related to the situation prevailing in the steady state flow picture of a small amplitude wind-generated gravity wave in - which the water flow represents the air flow in nature, while the "fixed in space" moving wavy boundary corresponds to the nearly constant water particle velocity at the surface of the wave. The results show that the normal stress distribution - over a moving boundary differs from that over a fixed one by a phase-lag with respect to the wave shape, which varies with the ratio of flow velocity to the boundary velocity (wave celerity), as predicted by the recent theories of Miles and Ben_ jamin. These results provide an explanation for the energy - transfer from wind to wave due to normal stresses and show that those experiments performed on fixed boundary models can not be associated with the phenomena of water wave generation.
Investigations have been undertaken to predict the tidal amplitudes and current patterns at the mouth of the Cano Macareo in Venezuela to the Atlantic Ocean. These studies were undertaken as part of a more comprehensive feasibility study sponsored by the Corporacion Venezolana de Guayana for location and orientation of a 60-foot deep navigation channel and for the design of related channel appurtenances. In the analysis, three simulation methods were employed conjunctively. These included oneand two-dimensional mathematical models and an electro analogical model. Model results have been supplemented with prototype data and other information based on field observations. Analyses provided for determination of tidal hydraulics, first, to establish baseline conditions as they presently exist, and second, to evaluate the effects of various proposed channel alignments. The twodimensional mathematical model and the electro analogical model both provided for inclusion of a pronounced longshore sea current which plays an important role in determining current patterns at the mouth of the Macareo. In addition, the use of a berm to modify the sea current in the vicinity of the channel entrance was investigated.
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