Principle Analysis And Development Of The Fiber Optic Sensor For Monitoring Subwater Topography Change

With the continuous development and utilization of river and marine resources, there are a large number of hydraulic structures in China. However, the erosive action of wave and flow will reduce the strength of the structures and cause the structural safety hazard. Due to the immaturity of sensor design, the accuracy of present monitoring sensors can not achieve very satisfactory results. It has restricted the real-time monitoring of hydraulic structures in our country.By the fiber grating sensing technology, we develop a sensor for monitoring subwater topography change based on the difference of lateral soil pressure between water and soil. The research contents are as follows:1. It is developed a method for monitoring subwater topography change that the sensors are installed in the vicinity of the hydraulic structures along the depth, which perceive environment of soil under the mud and water above the mud. According to the environment that sensors perceive, water-soil interface is distinguished.2. It is proposed the monitoring principle of the difference in the lateral earth pressure between water and soil:The horizontal pressure in soil consists of lateral earth pressure and pore water pressure, while that in water is water pressure only. As long as the measurement of the lateral earth pressure is obtained under a certain depth of the water, it can be judged the environment at the depth position.3. There are three kinds of sensor structure designed:diaphragm type sensor, equal intensity beam sensor, amplifier micrometer sensor, whose samples are produced.4. The performance tests for sensors are carried out by water standard method, sand standard method and water pressure stability test. Then the sensor structure is optimized.5. Considered with adverse sea condition, it has special treatment and protection for the sensor surface and transmission cable, and constructs scour depth monitoring system primarily.After the performance test and structure optimization, amplifier micrometer sensor is selected because of good work performance. On this basis, the scour depth monitoring system is constructed primarily, which realize the capability of remote real-time monitoring automatically. It can accurate feedback the subwater topography change of hydraulic structures, and provide effective data and early warning for the safe operation of hydraulic structures.