| Summary: | 碩士 === 崑山科技大學 === 機械工程研究所 === 101 === Optical fiber sensor technology is an applied technology that combines materials science, mechanics, optical electronics, and analytical instruments. Optical fiber is used as a conducting medium for light because it is high speed, low loss, broadband, corrosion-resistant, made with fine wire, resistant to electromagnetic interference, highly flexible, and has a wide range of applications. In current experiments, optical fiber can be used to test changes in pressure, temperature, acceleration, gas, and strain. Using an optical fiber sensor, this research explored and analyzed the micronutrient changes in the exterior of a pipe caused by an increase in the pressure of the flow within the pipe. We also experimented with the yield point of the pipe under strain by continuously increasing the pressure in the pipe in order to understand the level of pressure resistance so that accidents will not occur when using pipes under overload conditions. In addition, in real environments, the extensions of or connections between pipes are not only produced using an integrated method; rather, the materials used not only take up space, but also reduce flexibility in the usage of pipes. Therefore, welding is most often used to complete an extension or connection of pipes. When pipe welding under high temperatures is conducted, materials near the weld bead produce changes in the mechanical properties of metal. Therefore, the strength of a welded pipe and that of the original material are bound to have differences. Because of this, we also carried out variance analysis on the strength and strain of straight pipes (non-welded) and welded pipes.
This experiment adopted four fiber Bragg grating (FBG) sensors with different frequencies and directly adhered them to a position ¼ away from the pipe and the axis and hoop of the center for measurement. The reflected signal of the FBG sensors indicated displacement changes in the peak values (dBm) of the energy of the light wave and the wavelength of the spectrometer. For every 5 bar increase in the pressure in the pipe, the axial sensor showed the peak value of the waveform moving approximately 0.019 nm to the right, and the hoop sensor showed the peak value of the waveform moving approximately 0.072 nm to the right. Under a 40 bar pressure increase, the axial peak value moved approximately 0.15 nm to the right, while the hoop peak value moved 0.58 nm to the right, showing a linear trend in terms of the peak displacement. The experiment also discovered that the variable values in the heat-affected zone next to the weld bead of a welded pipe are greater than those in the non-heat-affected zone. This proves that the material properties of metals will change under high-temperature processing.
This experiment first applied optical fiber sensor technology to measure the flow in pipes under pressure strain. Related technologies can also be applied in the long-term monitoring of pipes to highlight the skillful, simple, and quick advantages of optical fiber.
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