| In recent years,the development of water resources has gradually shifted to the Northwestern and Southwestern of China.Moreover,the water sources have great potential value in many applications,such as flood control,power generation,irrigation,et al.However,the situation of alpine region is complex and winter lasts for a long time,resulting in some hydraulic structures,such as reservoir and hydropower station,often threatened by static ice pressure in winter.Therefore,it is great significance to study the changes of static ice pressure in the process of ice generation and dissipation for the conversion of water resources into actual productivity in cold regions.There is a problem that the change of pressure can not be obtained continuously in the process of generation and elimination.The paper set up a sensing system by combing fiber loop ring down spectroscopy(FLRDS)technology and field programmable gate array(FPGA)pulse modulation technology to carry out the two-channel test experiment,and using this sensing system to conduct a preliminary test on the static ice pressure.These experiments are mainly aimed at exploring the change stress on the bottom and side walls of the boundary in the process of ice generation and dissipation,and it proves that the system has the functions of the continuous detection.The paper mainly completed the following four works:1.Based on the continuous detection of the change of static ice pressure,the paper analyzed present situation of static ice pressure and detection technology of pressure after consulting a large number of documents.The paper proposed a method to measure static ice pressure.The method used optical fiber as strain sensing unit.The key of method was FPGA modulation technology and fiber loop ring down technology.2.This paper proposed a method of pulse modulation based on the principle of electro-optic modulation.This method used direct digital synthesis(DDS)and phase lock loop(PLL)frequency doubling based on FPGA to generate electrical pulses,respectively.The phase locked loop frequency doubling technology based on FPGA is used to generate electric pulse with adjustable pulse width and period for considering pulse width and complexity of circuit design.Electro-optic modulator is modulated by electric pulse,and could generate optical pulse with the narrowest pulse width of 5 ns.Optical pulses with adjustable pulse width and period provided a basis for the design of fiber loop.3.The paper used dual-channel displacement detection to verify feasibility of multichannel detection.According to the principle of parallel multiplexing,a dual multiplexing optical fiber sensor system based on FLRDS technology was built by using delay line technology.The system conducted detection experiment of fixed point displacement of sensing optical fiber.In addition,the repeatability and sensitivity of the sensor were studied.In experiments of shifting detection at fixed points of two channels,the ring length of A and B channels are 47.00 m,the delay line difference between them was 28.61 m.The phase difference of ring-down pulse was very obvious.The results showed that pulse overlap was not occur,which ensured the possibility of dual-channel detection.Besides,experimental results on repeatability of A and B channels showed that sensors had good repeatability and the results of the calibration experiment showed that the sensitivity of the two sensors was also very similar.In the validation experiment,the errors of channel A and B were 2.1% and 4.0%,respectively.4.The paper completed the static ice pressure measurement experiment of bottom and side wall based on the displacement measurement experiment of two fixed points.Experimental results of bottom static ice pressure measurement indicated the variation of static ice pressure could be roughly divided into three stages: growth stage,stable stage and decline stage in the process of ice generation and dissipation under the condition of room temperature of 19.8°C and icing environment of-12.5°C.The static ice pressure tended to increase in growth period when the temperature is below-2.1°C.During the stable period,the static ice pressure remained unchanged.However,the static ice pressure would decrease slightly between the growth period and the stable period.In the early stages of the decline period,the static ice pressure would also increase slightly until the temperature rose to 0°C,and the static ice pressure would increase to the maximum,with a value of 154.55 KPa.The reason was temperature rise rate.The static ice pressure decreased rapidly in the later stage of the decline period.The results showed that the static ice pressure on the side wall was higher than that on the bottom under the same experimental conditions in the experiment of side wall pressure measurement.Similarly,the static ice pressure on the side wall increased first and then remained unchanged.The static ice pressure would increase in the early stage of the descending period.The static ice pressure would decrease rapidly to 0KPa after 0°C.At the same time,the depth was different and the side wall pressure was different,and static ice pressure tended to decrease with increasing depth. |
