Abstract

The dynamic response of a flexible cylinder in a steady flow is investigated experimentally. The flexible cylinder with an aspect ratio of 145 is vertically installed in a water flume with about one-third of its bottom part submerged in the water. Uniform flows are generated in this test and the Reynolds number ranges from 1,290 to 2,710. With the aid of an advanced optical measurement device and the 3-D reconstruction technique, the vibration history of the cylinder is successfully obtained with high resolution. The variation of the displacement with the reduced velocity shows a clear lock-in regime. The spatial distribution of displacement and the spectrum analysis indicate that at least second-order mode is stimulated in the vortex induced vibration (VIV) response of the cylinder.

Introduction

Vortex induced vibration (VIV) of cylindrical structures has been a hot research topic in recent decades, due to its significance in engineering applications. Comprehensive reviews of the recent studies on VIV have been conducted by Sarpkaya (2004) and Williamson (2004). Many experimental studies on the response of elastically supported rigid cylinders in fluid flow have been performed, such as Khalak and Williamson (1999), Govardhan et al. (2000), Bourdier and Chaplin (2012). The response of flexible cylinder, which is a cylinder made of homogeneous elastic material, has gained increasing attention in recent years. Some of these representative studies on this topic include Chaplin et al. (2005), Trim et al. (2005), Baarholm et al. (2006), Huera-Huarte and Bearman (2009, 2014a). However, it is still very complex to measure the dynamic response of a flexible cylinder in the laboratory test. The common approach is to measure acceleration or strain first, mostly using Fiber Bragg Grating (FBG) and calculate the displacement using the modal decomposing technique. These embedded sensors are usually consumable, and a complicated design for the test model is needed to avoid disturbing the flow field and modifying the dynamic characteristics of the model itself.

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