This paper aims to realize the structural safety monitoring of protective engineering by conducting experimental research on the application of fiber optic grating sensors in high-speed penetration and damage monitoring. The study designs a miniaturized flexible fiber optic grating strain sensor for dynamic strain measurement during high-speed penetration and damage of the target body by projectiles, and verifies its measurement performance by comparing it with strain gauges. The experimental results demonstrate that the dynamic strain measurement results of the fiber optic grating strain sensor during high-speed penetration and damage are consistent with those of the strain gauges and the actual situation. The fiber optic grating strain sensor can achieve dynamic strain measurement during high-speed penetration and damage processes. Moreover, the variance of strain measurement results from the fiber optic grating strain sensors is much smaller than that of the strain gauges. This study validates that fiber optic grating strain sensors have the advantages of convenient installation, suitability for embedding, no need for electrical power, safety against explosions, immunity to electromagnetic interference, and strong environmental adaptability. They provide comparable results to strain gauges for measuring highspeed dynamic strains while overcoming the challenges associated with strain gauge installation difficulties, susceptibility to damage during embedding, high grounding requirements, poor environmental adaptability, and high surface bonding requirements. Therefore, fiber optic grating strain sensors are an important new technological approach that can replace strain gauges in future safety and health monitoring of protective engineering projects during wartime.
In this paper, we introduce our recent progress in resolution improvement of distributed temperature sensors by employing narrow pulse laser and wideband avalanche photoelectric detector (APD). The narrow pulse laser generates the light pulse with 4 ns with at its half maximum, which represents 40 cm spatial resolution. the wideband APD is employed to acquire the backscattering light at Raman wavelength and meet the need of spatial resolution of the narrow pulse laser. High spatial resolution is attributive to narrow pulse width, but also leads to the deterioration of the signal to noise ratio of demodulated temperature curve. Thus the APD with both high sensitivity and wideband width is employed to achieve high SNR and high spatial resolution. Temperature tests were taken out to evaluate the performance of proposed sensor. Results showed that the performance of our proposed spatial resolution enhanced distributed temperature sensor could achieve the temperature error of 1.2°C, temperature resolution of 0.49°C, sensing length of 1 km and spatial resolution of 0.5 m.
The application of distributed Brillouin optical fiber sensing technology in dam health monitoring is mainly studied in this paper. In the dam health monitoring system, the key technology is real-time deformation monitoring. Firstly, the principle of Brillouin optical time domain analysis (BOTDA) is introduced. A long-term on-line monitoring scheme of dam strain is proposed based on the distributed Brillouin sensing technology. The scheme includes cable layout and strain test. In the test, a 200m single-mode optical cable is selected. Firstly, the center frequency shift data of the whole optical cable is measured, when the displacement load is set to 0 mm, which is used as the test reference of strain variation. Then, the 2m length of the middle part of the optical cable is stretched to perform large amplitude tensile tests and shrinkage tests. The displacement loads are 2mm, 4mm, 6mm, 8mm and 10mm respectively. Next, small amplitude tensile tests and shrinkage tests are performed. The displacement load is 0.5mm, 1mm, 1.5mm and 2mm respectively. Analysis of test data shows that, the strain measurement range of the scheme can reach ± 4500με, the resolution of the scheme can reach 20 με. The results prove that the distributed fiber Brillouin sensor system can realize the long-term on-line distributed measurement of dam strain, which meets the requirements of the dam strain monitoring. It provides an effective means for dam health monitoring and protection, and a strong support for large-scale structural health monitoring with distributed Brillouin optical fiber sensing.
The application of distributed optical fiber sensing technology in nuclear island safety monitoring is mainly studied in this paper. The anti-radiation ability of the system is an important index. The distributed optical fiber system in this paper is designed with a special anti-radiation optical fiber. The temperature of power supply cables and other facilities in the nuclear island containment can be distributed monitored in full period in real time. Radiation tests are carried out to validate the anti-radiation performance of the system. 60Co is used as a gamma ray radiation source to generate continuous pulses with an average energy of 1.25 MeV. The rate of radiation dose is 1800 Gy/h and the total radiation dose is 1950 Gy. The anti-radiation ability of anti-radiation optical fiber and common optical fiber is compared. It is proved by tests that common optical fiber sensor has great fiber loss in radiation environment, about 0.5dBm, and the loss is decreasing continuously. Anti-radiation optical fiber has little fiber loss in radiation environment, about 0.12 dBm, and the loss tends to be saturated. During the radiation test, the temperature measurement performance of the distributed optical fiber sensing system using anti-radiation optical fiber and the one using common optical fiber is tested in real time. The results show that the anti-radiation distributed optical fiber sensing system performs well in the whole process, which meets the requirements of temperature monitoring for 1339.2 Gy total radiation dose in the refueling cycle of nuclear island.
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