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Appl. Sci. 2017, 7(2), 198; doi:10.3390/app7020198

Experimental Investigation on Soft Galloping and Hard Galloping of Triangular Prisms

1
State Key Laboratory of Hydraulic Engineering Simulation and Safety, Tianjin University, Tianjin 300072, China
2
Department of Civil Engineering, Case Western Reserve University, Cleveland, OH 44106, USA
*
Author to whom correspondence should be addressed.
Academic Editor: César M. A. Vasques
Received: 15 November 2016 / Revised: 19 January 2017 / Accepted: 13 February 2017 / Published: 17 February 2017
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Abstract

The studies currently on soft galloping (SG) and hard galloping (HG) are scarce. In this study, SG and HG of spring-mounted triangular prisms in a water channel are investigated experimentally. A power take-off system (PTO), a spring system, additional weights, and different triangular prisms were used to achieve the variations in damping coefficient c, system stiffness K, oscillation mass m and section aspect ratios α, respectively. The present paper proves that the VIV (vortex-induced vibration) lower branch can be observed in the SG response. In SG response, VIV branches are incomplete while the galloping branch is complete, and galloping can be self-initiated only in the self-excited region. On the contrary, in HG response, VIV branches are complete, the galloping branch is incomplete, and galloping can only be initiated by external excitation at a velocity exceeding the critical velocity. As c and m increase, or K and α decrease, the oscillation mode of a triangular prism gradually transitions from SG to CG (critical galloping), and continues to HG. The amplitude in VIV branch is the main reason causing the onset of galloping in SG response. A critical damping coefficient cc, which is dependent on m, K and α, is proposed to predict the occurrences of SG, CG and HG. When c < cc, SG occurs; when c > cc, HG occurs; when c = cc, CG occurs. View Full-Text
Keywords: triangular prism; flow-induced motion; damping; stiffness; mass; section aspect ratio triangular prism; flow-induced motion; damping; stiffness; mass; section aspect ratio
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Lian, J.; Yan, X.; Liu, F.; Zhang, J.; Ren, Q.; Yang, X. Experimental Investigation on Soft Galloping and Hard Galloping of Triangular Prisms. Appl. Sci. 2017, 7, 198.

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