The Identification of Power-In Region in Vortex-Induced Vibration of Flexible Cylinders

Abstract

This paper proposes a novel method to identify the power-in regions of long flexible cylinders subjected to vortex-induced vibration (VIV). It also attempts to address a practical problem: “Will a secondary power-in region appear after the primary power-in region is covered with suppression devices?” The source of data is a recent model test on a 38 meter long flexible cylinder, densely instrumented with fiber optic strain gauges and accelerometers. For pipes with partial coverage of suppression devices in uniform flow, the bare region would be expected to be a power-in region and the section with suppression devices is expected to be a power-out region. Experimental data from these types of tests are used to benchmark the proposed power-in zone identification method. The method is then used to identify the power-in zones on a bare cylinder in a sheared flow. This paper also explores the occurrence of secondary power-in regions that may exist, when suppression devices are placed in the primary power-in zone. Secondary power-in regions were observed. Lessons learned from the power-in region identification in sheared flows will be a useful tool for designer/engineers choosing where to place suppression devices.