In a recent article published in Scientific Reports, researchers introduced a novel method for measuring water velocity in open channels and rivers using optical fiber sensors. These sensors were based on fiber Bragg gratings (FBGs).
They described the design, simulation, and experimental validation of the FBG sensors, which offer precise, nonintrusive, and effective monitoring of water flow in various applications.
Study: Optical fiber sensor for water velocity measurement in rivers and channels. Image Credit: Jhampier Giron M/Shutterstock.com
Background
Water velocity is a crucial parameter for many applications involving water flow in open channels and rivers, including irrigation, flood control, hydropower generation, and water quality assessment. However, measuring water velocity is challenging due to the need for accurate, reliable, and nonintrusive devices.
Traditional methods, such as mechanical or electronic flow meters, have limitations, including high cost, maintenance requirements, the need for calibration, and potential interference with the flow.
Optical fiber sensors offer a promising alternative. They are based on light transmission and reflection, making them unaffected by the water environment.
Additionally, they can measure velocity at different locations along the fiber, providing a spatial resolution that other methods cannot achieve.
About the Research
In this paper, the authors designed, developed, and tested an optical fiber sensor for water velocity measurement based on FBGs, which are periodic variations of the refractive index of the fiber core. When light was launched into the fiber, the FBGs reflected a specific wavelength that depended on the strain applied to them.
The strain could be determined by measuring the wavelength shift of the reflected light. This strain is caused by the hydrodynamic force of the water flow on the fiber, which is related to the water velocity by fluid dynamics equations. Therefore, by measuring the strain, the water velocity could be calculated.
The researchers used two types of coatings for the FBGs: acrylate and aluminum. The acrylate coating is the standard one used for communication fibers, while the aluminum coating is more resistant to corrosion and rust in high-humidity environments.
They also used different diameters for the coated fibers: 250 micrometers for the acrylate and 180 micrometers for the aluminum.
The sensor's performance was tested under laboratory and field conditions using different flow rates, channel slopes, and sensor heights.
Additionally, the study compared the results with those obtained by several commercial methods, such as the Venturi flowmeter, an electromagnetic flowmeter, and a mechanical flowmeter, which are considered high-accuracy devices.
Research Findings
The outcomes demonstrated that the optical fiber sensor measured water velocity accurately and repeatedly. It showed a linear response to water velocity, with the wavelength shift proportional to the fiber strain.
The sensor's performance aligned well with theoretical calculations, computational simulations, and a commercial flow meter. Furthermore, the authors observed superior performance of the aluminum coating over the acrylate coating, noting lower hysteresis and higher sensitivity.
Additionally, the sensor effectively captured velocity distribution across the channel cross-section, revealing higher velocities at the center and near the water surface, and lower velocities near the channel walls and bottom.
Applications
The newly developed sensors have potential implications for measuring water velocity in open channels and rivers, offering benefits across various fields, including environmental monitoring, hydraulic engineering, and water resource management.
They provide crucial information about water flow conditions, such as velocity, discharge, and turbulence, which are essential for understanding water quality, sediment transport, and aquatic ecosystems.
These sensors can help design and optimize hydraulic structures like dams, weirs, spillways, and canals by accurately measuring water flow parameters and assessing hydraulic performance and efficiency.
Furthermore, they support the planning and operation of water supply and distribution systems, including irrigation, drinking water supply, and wastewater management, by monitoring water flow rates and volumes to ensure efficient use of water resources.
Conclusion
In summary, the novel approach was effective for measuring water velocity. It was more accurate and robust compared to state-of-the-art methodologies and offered advantages such as high sensitivity, fast response, immunity to electromagnetic interference, and the ability to measure velocity at multiple points simultaneously.
It could be integrated with other optical fiber sensors, such as those for measuring temperature, turbidity, hydrogen (pH) potential, and dissolved oxygen (O2), to provide a comprehensive and reliable monitoring system for water resources.
The authors suggested developing more secure and robust designs for long-term measurements, optimizing the calibration and maintenance procedures, and integrating the sensor with other optical fiber sensors for velocity measurement at several locations along the channel or river.
Journal Reference
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