Experimental analysis on vortex-induced vibration of a rigid cylinder with different surface roughness

摘要

This project presents an experimental work on vortex-induced vibration(VIV)of a short rigid cylinder to obtain its dynamic responses in cross-flow directions with different cylinder surface roughness.In order to enable the rigid cyhnder to suspend and vibrate freely upon excitation of wind speed,a supporting structure has been designed and fabricated.This paper aims to investigate the effect of cylinder surface roughness on the characteristics of VIV.The surface roughness was differentiated by using two grade sizes of sandpapers.This self-designed experiments were conducted using Wind Blower at Aeronautical and Wind Engineering Laboratory(AEROLAB),UTM Kuala Lumpur.By using the accelerometer,the raw amplitude readings were recorded and processed using LMS TestXpress 12 software.The data was recorded in the range from 1 m/s to 8 m/s of wind speed,with an interval of 1 m/s.Analysis on the data in terms of amplitude and frequency responses was conducted to identify the effect of cylinder surface roughness on the characteristics of VIV.The lock-in region is found at the low reduced velocity range,where the amplitude value is slightly higher.At Vr=8 lock in phenomena is occurred.From the results obtained,the amplitude increases as the vortex shedding frequency close to the natural frequency of the cylinder,where the frequency ratio =1.Amplitude reduction is found to be 86.7% and 3.43% for the highest and middle surface roughness respectively.The higher the surface roughness,the higher the amplitude reduction.