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Descripción
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| Vibrations can induce a range of different interfacial phenomena in fluid systems depending on the frequency and orientation of the forcing. With gravity, (large) interfaces are approximately flat and there is a qualitative difference between vertical and horizontal forcing. Sufficient vertical forcing produces subharmonic standing (Faraday) waves that extend over the entire interface. Horizontal forcing can excite both localized and extended interfacial phenomena. In the case where the interface separates two fluids of different density in, for example, a rectangular container, the mass transfer due to vertical motion near the endwalls requires a counterflow in the interior region that can cause a Kelvin-Helmholtz type instability and a ``frozen wave" pattern. In microgravity, the dominance of surface forces favors non-flat equilibrium configurations and the distinction between vertical and horizontal applied forcing can be lost. Furthermore, the vibrational field contributes a dynamic pressure term that competes with surface tension to select the (time-averaged) shape of the surface. These modified (quasi-static) surface configurations, known as vibroequilibria, can differ substantially from the hydrostatic state. In fact, there is a tendency for the interface to orient perpendicular to the main vibrational axis, which can be considered as a type of artificial gravity. In some cases, a bulge or cavity is induced that leads to splitting (fluid separation). We investigate the interaction of these prominent interfacial instabilities in the absence of gravity, concentrating on harmonically vibrated rectangular containers of fluid. We compare vibroequilibria theory with direct numerical simulations and consider the effect of surfaces waves, which can excite sloshing motion of the vibroequilibria. A saddle-node bifurcation occurs with increasing forcing on the branch of symmetric singly-connected vibroequilibria solutions for sufficiently deep containers. The interaction of vibroequilibria and frozen waves is considered. Microgravity experimental results from the ``Control of Fluids in Microgravity with Vibrations'' (CFVib) experiment, which flew on the 65th ESA Parabolic Flight Campaign as part of the 2016 Fly Your Thesis! programme, are described as well. This experiment had cuboidal and cylindrical containers containing water/air, silicone oil/air or silicone oil/vacuum oil mixtures. Half of the containers were subjected to vibrations using a piezoelectric bender beam assembly that generated high-frequency vibrations from 50 Hz to 12 kHz. The primary objective was to observe the behaviour of vibrated liquids in a weightless environment and to investigate the extent to which vibrations could be used to influence and control this behaviour. Surface waves and large-scale reorientation of the interface were observed, depending on the frequency. For cuboidal containers with water, particularly good agreement was found between the experimental data and the predictions of vibroequilibria simulations. | |
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Internacional
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No |
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Nombre congreso
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42nd Scientific Assembly of the Committee on Space Research (COSPAR) |
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Tipo de participación
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960 |
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Lugar del congreso
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Pasadena, California, EE.UU. |
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Revisores
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Si |
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ISBN o ISSN
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11-1111-111-1 |
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DOI
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Fecha inicio congreso
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14/07/2018 |
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Fecha fin congreso
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22/07/2018 |
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1 |
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x |