Fiber Grating Vibration Acceleration Sensor Optimization Design And The Modal Analysis For The Body Of The Vibration

With the development of the technology, the traffic of our country has been rapidly developed in21century. In the national scope, many roads, bridges, and high-speed railways are built. However the monitoring of these large structures is still a vacancy, which makes the structures damage can’t be found in time. The damage is accumulated and leads to the collapse accident, which often results in significant casualties and huge economic losses. To avoid this kind of accident, the prompt and accurate detection of damage to buildings is particularly important. Therefore, optical fiber grating acceleration vibration sensor for the detection of buildings is mainly studied is this paper. The damage identification technique based on natural frequencies is also studied, and a set of simple, accurate detection method is proposed.A new vibration sensor based on the double strength cantilever beam fiber Bragg grating is demonstrated. First, the sensor is conducted numerical calculation and simulation by ANSYS software. The amplitude-frequency and phase-frequency characteristics curve of sensor in each damping ratio is obtained. Through changing the parameters of the sensor structure, sensor optimal structure parameters are got, which can make the sensor having the best resonance frequency and acceleration sensitivity. Second, sensor is fabricated based on the optimal structure parameters. Finally, the sensor is studied by shaking table test. The experimental results show that the resonant frequency of the developed vibration sensor is80.74Hz, and the acceleration sensitivity is about20.85pm/m·s-2. Amplitude-frequency characteristics of the sensor in the5-50Hz frequency range shows a flat horizontal line. The proposed sensor is suitable for the low-frequency(5-50Hz) vibration signal detection.The general methods of damage identification are introduced in this paper, the relationship between monitoring health conditions and inherent frequency is explicit. The four groups of bridge model are man-made damaged, of which have the same structure size and material. The damage extent of each is different. In the same experiment of these four groups of bridge model, the relationship between the damage degree of monitoring objects and natural frequency is obtained. When the damage degree increases, the natural frequency will decrease. Through ANSYS software, the four groups of bridge models are establishedand simulated. The analysis gives the natural frequencies of the bridge under differentdamage degree. It shows that damage degree increases with natural frequency decreases,which matches the experiment result. Therefore, when the bridge is damaged, naturalfrequency decreases.