Analysis of Self-excited Sloshing Caused by the Fluid Discharge over the Flexible Weir Including Nonlinearity

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Two rypes of self-excited vibrations of a cylindrical shell caused by the fluid discharge over the flexible weir were observed in French demonstration fast breeder reactor, Super Phoenix-1 during test operations. The first type is a sloshing coupled vibration and the latter is so called a fluidelastic vibration.In this study, an analytical model for the sloshing coupled vibration as observed in Super-Phoenix-ILMFBR is proposed. This fluid-structure system is constituted by the flexible weir and adjoining fluid plenums and the fluid is discharged from the upstream plenum to the downstream plenum over the flexible weir. The characteristic equation of the system is derived for the case in which the weir vibrates at the frequency of the downstream sloshing.In this research project, special attentions were made with higher mode sloshing coupled vibrations with the case of a rectangular flexible plate and with the case of two flexible cylindrical weirs. The effects of the fluid level difference between the upstream and the downstream plenum and weir rigidity are examined both theoretically and experimentally and the mechanism for instability is discussed in detail. As a result, it was found that the effects of discharge flow rate and the liquid height difference between the upper and lower tank on the higher mode instability can also be described by the proposed analytical model.