Multiplexed fiber optic pressure and vibration sensors for hydroelectric dam monitoring

The area of embedded sensors for performance and health monitoring of critical structures such as dams represents a logical extension of earlier efforts in applications of fiber optic sensors. We have been most fortunate in having a 7.5+ MW hydroelectric dam beginning construction on the Winooski River here in Vermont. Based on our work in embedding sensors into the Stafford Building, the idea of embedding sensors into the concrete superstructure of a hydroelectric dam seemed most noteworthy. We are modifying photoelastic (or polarization) based fiber optic pressure sensors while allowing the multiplexing of up to 10 sensors onto each of separate multimode fibers. The modifications entail varying the physical packaging of the sensor's components for better meshing with the dam's rebar-concrete configuration. The individual sensors will be interrogated via optical frequency domain (chirped) techniques to provide a total of 50 discrete pressure readings along the dam's 15 m (high) by 160 m (long) surface. A number (probably 12, chosen because of materials costs) of fewmode and multimode embedded fiber optic vibration sensors are also being developed for embedding in the immediate area surrounding the hydroelectric turbines. We will then be able to determine the dam structure's frequency response as the turbines are subjected to varying electrical and water loads. By relying on our prior experience with using embedded sensors for communications and sensing, we will attempt to also analyze the multiplexed upstream- surface embedded fibers to determine if we can also use those fibers to perform vibration studies. The results and/or plans for this project will also be presented.