UBC Theses and Dissertations
A study of electrically driven standing waves on fluid surfaces Ionides, George Nicos
The properties of standing surface waves on conducting liquids (mercury and water) have been studied in conditions where the waves are excited by electric fields applied normally to the free surface of the fluids. The fields are spatially non-uniform, static and periodic in time. The amplitudes on mercury were measured by observing the shift of the resonant frequency of a microwave resonator containing the mercury; an optical technique was used for water. Both methods permit wave amplitudes to be measured to an accuracy of 5 x 10⁻⁴cm. The decrease of frequency of small amplitude (~0.005 cm), linearized waves has been examined for mercury in a cylindrical container, as a function of the strength of an applied electrostatic field. The results are in close agreement with an appropriately modified uniform field theory. Observations on the damping of surface waves show that strong electrostatic fields (up to 55 kV/cm) do not affect the boundary layer structure at the fluid surface. Single surface wave modes- have been excited by applying electric stresses at the displacement antinodes of a desired mode, and setting the period of the applied stress equal to the natural mode period. When the surface mode amplitude becomes comparable to the mean distance from the field applying electrode to the fluid surface, the driving force depends on the wave amplitude, and is non-linear. The non-linearity produces an overstable surface. New stability criteria are formulated, which agree well with observations. Non-linear mixing of surface modes on shallow water has also been studied, and the exchange of energy among surface modes conclusively demonstrated. Viscous dissipation was taken as the amplitude limiting factor, and the results are in good agreement with theory.
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