Static Ice Pressure Measurement Based On Fiber Loop Ring Down

In the northeast,northwest and other regions of our country,the damage to the hydraulic structures and economic losses often occur because of the large area ice in winter.Therefore,it is necessary to study the ice mechanical characteristics and understand the change of force in ice growth and melting process,and it can provide guidance for the protection and construction of hydraulic structures.With the development of optical fiber technology,optical fiber sensor technology has developed rapidly over the past 50 years and been used in many fields because of its simple structure,anti-electromagnetic interference,small size,high sensitivity and so on.Fiber loop ring down(FLRD)technology is a kind of intensity modulation technology based on cavity ring down spectroscopy(CRDS).Optical fiber sensor based on FLRD technology also has good stability,real-time performance,fast response and so on.In this paper,a continuous monitoring system of static ice pressure is designed based on FLRD and fiber micro-bend sensor technology.The main work of this paper includes:(1)Through reviewing the literature,this paper summarizes the research status and estimation methods of static ice pressure,and introduces the basic principle and classification of optical fiber sensing.(2)This paper introduces the basic structure,principle and development process of CRDS and FLRD technology.FLRD technology consists of pulse light source,optical fiber loop,and the data processing section.The pulse light source uses an erbium-doped fiber ring mode-locked laser built in our laboratory.The fiber loop consists of two 2×1 fiber couplers with the splitting rate of 95: 5 and a piece of single mode fiber.The date processing section contains a photodetector and an oscilloscope.FLRD technology measures the ring down time of the pulse in the fiber loop,rather than measuring the intensity in the conventional sensor,so it can avoid the error caused by the light intensity jitter.(3)Through the discussion of the fiber bending loss theory and the microbend sensor’s sensitivity,we design the micro-bend sensor using a 3-D printer for static ice pressure measurement.(4)We design a static ice pressure sensor system based on FLRD and fiber micro-bend principle.The static ice pressure during ice growth and melting from-10 ℃~6 ℃ is monitored by the system with a temperature and humidity testing chamber.Sensitivity of 0.00998 /(μs·k Pa)is achieved and the max pressure(552±4)kPa is measured.Experiments show that this sensor system can monitor the whole ice growth and melting process continuously and in real-time.