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Descripción
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| Guard cables, also named ground cables, protect the overhead power lines from electrical discharges that occur during storms. They are installed above the power conductor and therefore, they are the highest cable installed. In some places they are provided with beacon spheres that are visible indicators used for identifying the overhead power lines, to warn low flying airplanes and helicopters of the obstructions. A new transverse aeroelastic instability that appears in guard cables with beacons when excited by a longitudinal wind (TILoW for short) has recently been reported to us. In some cases, a vertical or horizontal oscillatory motion takes place, whereas in other cases the beacon centers follow circular orbits placed also in the transverse plane, while each beacon follows the motion but remaining parallel to itself. The centers of the orbits seem to be close to the static equilibrium position of the guard cable catenary. This whirling motion can be identified as a kind of autorotation. In this work the instability is described, and vortex induced vibration (VIV) is suggested as a candidate responsible for the aerodynamic force exciting the oscillation modes. For the whirling (also could be denoted ?revolving?) mode a parallel investigation is ongoing. In order to clarify the problem, a model of the elastic configuration that is excited by the aerodynamic loads is analyzed, the eigenmodes and eigenvalues are presented, and a preliminary order of magnitude assessment of the field data is performed. Frequencies and mode shapes derived from the elastic model and those from the video sequences are found to be in agreement. The oscillation results are compatible with the existence of an alternating force produced by vortex shedding from the sphere. Unfortunately, the assessment could not be pursued further due to the absence of data on the wind speed during the reported sequences. A simplified model of the cable with only one beacon (a swinging sphere) has been tested in a low speed wind tunnel, and the main modes (VIV oscillation and whirling autorotation) have been reproduced and characterized. | |
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Internacional
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Si |
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JCR del ISI
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Si |
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Título de la revista
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Journal of Fluids And Structures |
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ISSN
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0889-9746 |
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Factor de impacto JCR
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2,021 |
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Información de impacto
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Datos JCR del año 2016 |
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Volumen
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DOI
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10.1016/j.jfluidstructs.2018.10.003 |
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Número de revista
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84 |
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Desde la página
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122 |
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Hasta la página
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139 |
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Mes
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SIN MES |
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Ranking
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Q1 |