Axial-flow-induced Vibration Of Cylinder Using FBG Sensor

As fossil reduces and oil price increases,more and more people pay attention to new power energy.Nuclear energy as a high production value energy is one of them.However,security of the utilization of the nuclear energy gets great concern.Chernobyl and Fukushima nuclear leakage accidents are terrible disaster to our living.In order to utilize nuclear safely,the security level of the nuclear energy should be enhanced.Except for nature disaster and man-made incident,axial flow induced vibration was a main reason leading to disaster.The amplitude of the vibration induced by axial flow was small.The fluctuation of the vibration amplitude was only about 10-3 to 10-2D.However,in the nuclear reactor,spacing between fuel rods was very small,little vibration may lead to abrasion,corrosion and erupt of the element crack in structure.The experiment was performed in Water Tunnel Laboratory at Harbin Institute of Technology Shenzhen Graduate School.The present parameters are different from the previous parameters due to the repair of the water tunnel.Thus,the calibration of the water tunnel needs to be repeated.The result of the calibration shows that the vibration of the wall of the water tunnel was 3.5 ?m maximum.The spectrum indicates that the nature frequency of the tunnel wall is 3.66 Hz.The vibration of the tunnel wall has little effect on the vibration of the cylinder by comparing their vibration amplitudes.The experiment aims to study the vibration of cylinder induced by axis flow.A Fibre Bragg Grating(FBG)sensor was introduced to measure strain of a flexible cylinder in axial flow.A laser vibrometer was used to calibrate the FBG sensor.The results indicate that the fluctuation of strain ?rms measured by the FBG sensor is consistent with the vibration amplitude Yrms measured by the laser vibrometer.When the amplitude of the cylinder vibration is small,the fluctuation of strain ?rms and the vibration amplitude Yrms are linearly related.Thus the FBG sensor can be used to measure the cylinder vibration induced by axial flow.The experiment first introduces the multi-point FBG system for flow induced vibration measurements.Using the cascaded FBGs,one can obtain the vibration information of different positions at the cylinder.Rotating the cylinder bonder with FBG sensor by 90o,we obtain the displacement signal in perpendicular plane.In addition,we study the vibration of the cylinder in different pitch of the cylinders.The results show that the decrease of pitch ratio can increase the vibration amplitude of flexible cylinder when the flexible cylinder is between two rigid cylinders.The smaller is the pitch ratio,the stronger is the effect.