Possibilities for Groundwater Flow Sensing with Fiber Bragg Grating Sensors

Abstract

An understanding of groundwater flow near drinking water extraction wells is crucial when it comes to avoiding well clogging and pollution. A promising new approach to groundwater flow monitoring is the deployment of a network of optical fibers with fiber Bragg grating (FBG) sensors. In preparation for a field experiment, a laboratory scale aquifer was constructed to investigate the feasibility of FBG sensors for this application. Multiparameter FBG sensors were able to detect changes in temperature, pressure, and fiber shape with sensitivities influenced by the packaging. The first results showed that, in a simulated environment with a flow velocity of 2.9 m/d, FBG strain effects were more pronounced than initially expected. FBG sensors of a pressure-induced strain implemented in a spatial array could form a multiplexed sensor for the groundwater flow direction and magnitude. Within the scope of this research, key technical specifications of FBG interrogators for groundwater flow sensing were also identified.

Dynamic Consolidation Measurements in a Well Field Using Fiber Bragg Grating Sensors

“…According to the results, if an FBG fiber in a teflon tube compresses/expands faster, it is more likely to show this relaxation behavior. Similar effects were previously observed by Drusová et al [13] in an aquifer simulator filled with uniform sand. When pore pressure/flow suddenly changed, FBG sensors with PVC and teflon coating both showed a relaxation response against the pressure changes.…”

“…The temperature from the liquid is coupled through the teflon tube that is housing the fiber-bundle. The temperature sensitivity coefficient is in this case α = 7.43 × 10 −6 K −1 [13], and temperature contribution to FBG response is ΔλTλ0=αΔT…”

“…In our previous study [13], we described the possibilities for groundwater flow sensing using another type of optical fiber sensors, Fiber Bragg Grating (FBG) sensors. An FBG sensor is a periodic modulation of refractive index in a fiber core.…”

“…Our previous research [13] showed that FBG sensors with a standard polyvinyl chloride (PVC) and teflon packaging already respond to pressure and flow changes in an aquifer simulator with natural flow. Pressure changes could be related to consolidation, while the mechanism of possible flow coupling is less clear.…”

Design of Flow Velocity and Direction Monitoring Sensor Based on Fiber Bragg Grating

“…The lower part is mainly composed of a cardan plate and a steering shaft. As shown in Figure 1, the components of the sensor are listed as follows: (1) venturi, (2) sliding connection, (3) eccentric wheel, (4) washer, (5) closed push rod, (6) displacement conduction shaft, (7) displacement top shaft, (8) strain grating, (9) wire, (10) nut, (11) steering shaft, (12) simple beam, (13) support frame, (14) frame base, (15) rolling bearing, (16) coding plate of shaft sleeve, (17) water turbine, (18) lever, (19) universal plate, (20) coding plate of shaft sleeve and (21) optical fiber Grating.…”