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Curr. Opt. Photon. 2022; 6(2): 137-142

Published online April 25, 2022 https://doi.org/10.3807/COPP.2022.6.2.137

Copyright © Optical Society of Korea.

Experimental Study on Leak-induced Vibration in Water Pipelines Using Fiber Bragg Grating Sensors

Dae-Gil Kim1, Aram Lee1, Si-Woong Park1, Chanil Yeo1, Cheolho Bae2, Hyoung-Jun Park1

1Honam Research Center, Electronics and Telecommunications Research Institute, Gwangju 61012, Korea
2Smart Water Research Center, K-water Research Institute, Daejeon 34045, Korea

Corresponding author: *spacegon@etri.re.kr, ORCID 0000-0002-8258-3224

Received: January 18, 2022; Revised: March 4, 2022; Accepted: March 4, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Leak detection is one of the most important challenges in condition monitoring of water pipelines. Fiber Bragg grating (FBG) sensors offer an attractive technique to detect leak signals. In this paper, leak measurements were conducted on a water distribution pilot plant with a length of 270 m and a diameter of 100 mm. FBG sensors were installed on the pipeline surface and used to detect leak vibration signals. The leak was demonstrated with 1-, 2-, 3-, and 4-mm diameter leak holes in four different pipe types. The frequency response of leak signals was analyzed by fast Fourier transform analysis in real time. In the experiment, the frequency range of leak signals was approximately 340–440 Hz. The frequency shifts of leak signals according to the pipe type and the size of the leak hole were demonstrated at a pressure of 1.8 bar and a flow rate of 25.51 m3/h. Results show that frequency shifts detected by FBG sensors can be used to detect leaks in pipelines.

Keywords: Fiber Bragg grating, Leak, Pipeline, Vibration, Water distribution network

OCIS codes: (060.2370) Fiber optics sensors; (060.3735) Fiber Bragg gratings; (120.7280) Vibration analysis

A water distribution network (WDN), which transports water efficiently, quickly, and economically, is an essential part of a country’s infrastructure. However, as WDN infrastructure grows and ages, pipelines are affected by aging, the environment, and third-party intrusion, resulting in defects such as leaks [1].

Various methods for detecting leaks in water pipelines, such as visual inspection, listening technologies using listening sticks and geophones, acoustic monitoring technologies using accelerometers and hydrophones, infrared thermography, and fiber optic technology, have been developed to ensure the safety, reliability, and efficient operation of WDNs [24]. However, since most pipes are buried underground, traditional sensors have difficulties in continuous monitoring due to problems such as moisture proofing, dust proofing, and sensor installation caused by environmental factors. Fiber optic technologies are suitable for real-time leak detection because of their inherent advantages: stability in harsh environments, small size, light weight, flexibility, corrosion resistance, and multiplexing ability [57]. In particular, fiber Bragg grating (FBG) sensors have been very successful in measuring strain, temperature, and vibration in various applications [813]. Thus, they can also be used to detect leak vibro-acoustic signals of pipelines in inaccessible areas of WDNs.

The vibration in pipelines of a WDN includes both longitudinal waves propagating in the axial direction of the pipe and transverse waves propagating in the radial direction, which leads to the fluid-pipe coupled vibration [14, 15]. The basic forms of fluid-pipe coupled vibration are the breathing mode (n = 0) and bending mode (n = 1). Since most pipelines are buried and constrained, it is difficult to detect vibration in the bending mode. The breathing mode induces the expansion and contraction of the pipe surrounding the water stream because of the pressure change caused by the water flows. In addition, in the event of a leak, the fluid sound propagates along the pipe, and the leak signal exists in a low-frequency band [15]. The detection of leak signals using FBG sensors particularly measures the radial component of breathing mode.

In this paper, we present results from leak vibration measurements performed on a water distribution pilot plant. The water distribution pilot plant consists of four pipe types made of different materials with a total length of 270 m. The leak was simulated by directly drilling a leak hole on the side, and FBGs were used as vibration sensors to detect leak vibro-acoustic signals. The recorded leak signals were analyzed by fast Fourier transform (FFT) in real time. At a pressure of 1.8 bar and a flow rate of 25.51 m3/h, the experiments revealed a frequency difference in the leak signal depending on the type of pipeline and the size of the leak hole.

The experiments were conducted on a water distribution pilot plant with a length of 270 m developed in the smart water research center of the K-water Research Institute. The water distribution pilot plant consists of straight pipes with a maximum length of 6 m, elbows, flanges, pipe supports, pumps, valves, etc., as shown in Fig. 1, and their dimensions and fluidic parameters are listed in Table 1. Four pipe types are installed, including a cement mortar lining ductile cast iron pipe (DCIP), which is the main pipe type buried underground, a polyethylene pipe (PE) as a plastic pipe, a steel pipe (SP) with epoxy inner coating and polyethylene outer coating, and a 30-year-old ductile iron pipe (DIP). Each pipe has an average length of 70 m and diameter of 100 mm. For the water circulation system, directional flow from the water reservoir to the pipelines is engaged by pump-generated pressure, and after the completion of circulation, the flow returns to the water reservoir.

TABLE 1 Specification of water distribution pilot plant

ParameterValue
Facility Area (m2)316
Pipe MaterialDCIP, PE, SP, DIP (old)
Total Length (m)270
Diameter (mm)100
Water Pressure<10 bar
Water Velocity (m/sec)0.07–2.0


Figure 1.Schematic of water distribution pilot plant. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.

To replicate pipe leaks, 1-, 2-, 3-, and 4-mm diameter leak holes were drilled into each surface of straight pipe segments in four monitored regions located in the middle of the pipeline (Fig. 1 and Fig. 2), and then tapping saddles were fastened as shown in Fig. 3(a). The tapping saddle can turn the water leak on and off using a valve [Fig. 3(b) and 3(d)]. Starting from one end of the pipe segment, four leak points were evenly spaced by approximately 50 cm (Fig. 2).

Figure 2.Fiber Bragg grating (FBG) sensor and leak points in monitored region.

Figure 3.Experimental layout: (a) leak simulator fastened with tapping saddle, (b) Leak hole, (c) FBG sensor bonded onto DCIP, (d) Water leak from 4 mm leak hole, and (e) FBG sensor interrogation system. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.

FBG sensors were used to detect vibro-acoustic signals in the four monitored regions. After removing foreign substances from the pipeline surface, FBG sensors were placed 1.2 m away from the starting point of the pipe segment [Fig. 2 and Fig. 3(c)] in each monitoring region and bonded with epoxy adhesive.

The distances from the FBG sensor to the 1-, 2-, 3-, and 4-mm leak points were 2.80, 3.30, 3.85, and 4.40 m, respectively. Four bare-type FBG sensors, with a reflectivity of 80%, an FWHM of 0.2 nm, Bragg wavelengths of 1550.37, 1555.05, 1560.78, and 1565.49 nm, respectively, were used in the experiment, as shown in Table 2. Fig. 3(e) depicts the FBG sensor system, which comprises a C-band erbium-doped fiber amplifier module with 40-nm (1530–1570 nm) 3-dB bandwidth and 17-dBm output power, an InGaAs photodiode array (PDA) module equipped with a volume phase grating and 512-px PDA, and an optical fiber circulator to demodulate the Bragg wavelength of the FBG sensors. The reflected Bragg wavelengths are fed to the InGaAs PDA through the circulator. Shifts in Bragg wavelength due to leak vibration can be measured using the PDA at a sampling rate of 3 kHz and analyzed by FFT.

TABLE 2 Monitored region and Bragg wavelength of fiber Bragg grating (FBG) sensors

SensorsMonitored RegionBragg Wavelength (nm)
FBG 1DCIP1550.37
FBG 2PE1555.37
FBG 3SP1560.78
FBG 4DIP (old)1565.49

To verify the performance of FBG vibration sensors, an acoustic signal was applied to the monitored region of the DCIP using an acoustic speaker for the simulation of leak-induced vibration while the pump was turned off, as illustrated in Fig. 4. As shown in Fig. 5, acoustic signals of 100–1000 Hz were applied at intervals of 100 Hz 3.9 m away from the FBG sensor, and the resulting vibro-acoustic signals were measured using the FBG sensor interrogation system for FFT analysis. The results showed that the FBG vibration sensor system can effectively measure vibro-acoustic signals applied by the acoustic speaker.

Figure 4.Layout for frequency measurement of FBG sensor.

Figure 5.Preliminary test of frequency shift measurement depending on speaker-induced acoustic signals.

Fig. 6 shows FFT analysis results according to different leak sizes in the four pipe types. For comparison, the measurement of a no hole case (none) was included as well. Twenty experimental cases are listed in Table 3. Pressure and flow rate were set to 1.8 bar and 25.51 m3/h, respectively, in compliance with the general pressure of a WDN (1.5–7 bar or 1.53–7.1 kgf/cm2) designated by the Korean design standard [16]. In the case of no leak, vibro-acoustic frequencies of 342 Hz for DCIP, 357 Hz for PE, 364 Hz for SP, 371 Hz for DIP (old) were detected.

TABLE 3 Experimental cases

Pipe TypeLeak Hole Size (mm)
DCIPnone; 1; 2; 3; 4
PEnone; 1; 2; 3; 4
SPnone; 1; 2; 3; 4
DIP (old)none; 1; 2; 3; 4


Figure 6.FFT results according to the leak size. (a) ductile cast iron pipe (DCIP), (b) polyethylene pipe (PE), (c) steel pipe (SP), (d) ductile iron pipe (DIP) (old).

When the leak size was increased to 1, 2, 3, and 4 mm, the peak frequencies at DCIP [Fig. 6(a)] were 384, 389, 395, and 394 Hz, respectively, at PE [Fig. 6(b)] were 390, 391, 395, and 397 Hz, respectively, and at SP [Fig. 6(c)] were 405, 410, 414, and 411 Hz, respectively, and at DIP (old) [Fig. 6(d)] were 392, 417, 411, and 414 Hz, respectively. As the leak size increased, it was confirmed that peak frequencies in all pipes increased as well by approximately 21–52 Hz compared to the case of no leak.

Fig. 7 summarizes the frequency shifts shown in Fig. 6, which ranged from 340 to 440 Hz due to the variation of the leak size. The peak frequency of all pipelines increased as the leak diameter increased, but it was difficult to distinguish the leak size. Frequency changes according to the leak diameter were approximately 10 Hz in DCIP, 6 Hz in PE, 9 Hz in SP, and 25 Hz in DIP (old). However, as soon as a leak occurred, the frequency in all pipes shifted significantly due to the pressure change. The shifts of peak frequency were 42 Hz in DCIP, 39 Hz in PE, 41 Hz in SP, and 21 Hz in DIP (old). It shows that frequency shifts can be used to detect leaks in pipelines.

Figure 7.Frequency shifts against the leak size.

In this paper, leak measurements were performed on a water distribution pilot plant using FBG sensors that were installed on the pipeline surface and used to detect leak vibration signals at a sampling rate of 3-kHz. The leak was demonstrated using four pipe types and 1–4-mm diameter leak holes with tapping saddles on the surface of the pipelines. The frequency response of the leak signal was analyzed by FFT analysis in real time. From the experimental results, the frequency range of leak signals was approximately 340–440 Hz at a pressure of 1.8 bar and a flow rate of 25.51 m3/h. When a leak occurred, the peak frequency of all pipelines tended to increase, but it was difficult to distinguish the leak size. However, as soon as the leak occurred, the peak frequencies in all pipes shifted significantly by approximately 21–42 Hz compared to the no leak case, which can be used to detect a leak in pipelines.

Future work will focus on using experimental data in the fiber optic-distributed acoustic sensing system, measuring the trend of vibro-acoustic changes of the components of WDNs, and implementing field tests of old pipelines or specific areas of smart WDNs, where risks are expected.

Data underlying the results presented in this paper are not publicly available at the time of publication, which may be obtained from the authors upon reasonable request.

This research has been performed as Project No Open Innovation R&D (20-A-T-002) and supported by K-water.

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  5. K. Ibrahim, S. Tariq, B. Bakhtawar, and T. Zayed, “Application of fiber optics in water distribution networks for leak detection and localization: a mixed methodology-based review,” H2Open J. 4, 244-261 (2021).
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Article

Article

Curr. Opt. Photon. 2022; 6(2): 137-142

Published online April 25, 2022 https://doi.org/10.3807/COPP.2022.6.2.137

Copyright © Optical Society of Korea.

Experimental Study on Leak-induced Vibration in Water Pipelines Using Fiber Bragg Grating Sensors

Dae-Gil Kim1, Aram Lee1, Si-Woong Park1, Chanil Yeo1, Cheolho Bae2, Hyoung-Jun Park1

1Honam Research Center, Electronics and Telecommunications Research Institute, Gwangju 61012, Korea
2Smart Water Research Center, K-water Research Institute, Daejeon 34045, Korea

Correspondence to:*spacegon@etri.re.kr, ORCID 0000-0002-8258-3224

Received: January 18, 2022; Revised: March 4, 2022; Accepted: March 4, 2022

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

Leak detection is one of the most important challenges in condition monitoring of water pipelines. Fiber Bragg grating (FBG) sensors offer an attractive technique to detect leak signals. In this paper, leak measurements were conducted on a water distribution pilot plant with a length of 270 m and a diameter of 100 mm. FBG sensors were installed on the pipeline surface and used to detect leak vibration signals. The leak was demonstrated with 1-, 2-, 3-, and 4-mm diameter leak holes in four different pipe types. The frequency response of leak signals was analyzed by fast Fourier transform analysis in real time. In the experiment, the frequency range of leak signals was approximately 340–440 Hz. The frequency shifts of leak signals according to the pipe type and the size of the leak hole were demonstrated at a pressure of 1.8 bar and a flow rate of 25.51 m3/h. Results show that frequency shifts detected by FBG sensors can be used to detect leaks in pipelines.

Keywords: Fiber Bragg grating, Leak, Pipeline, Vibration, Water distribution network

I. INTRODUCTION

A water distribution network (WDN), which transports water efficiently, quickly, and economically, is an essential part of a country’s infrastructure. However, as WDN infrastructure grows and ages, pipelines are affected by aging, the environment, and third-party intrusion, resulting in defects such as leaks [1].

Various methods for detecting leaks in water pipelines, such as visual inspection, listening technologies using listening sticks and geophones, acoustic monitoring technologies using accelerometers and hydrophones, infrared thermography, and fiber optic technology, have been developed to ensure the safety, reliability, and efficient operation of WDNs [24]. However, since most pipes are buried underground, traditional sensors have difficulties in continuous monitoring due to problems such as moisture proofing, dust proofing, and sensor installation caused by environmental factors. Fiber optic technologies are suitable for real-time leak detection because of their inherent advantages: stability in harsh environments, small size, light weight, flexibility, corrosion resistance, and multiplexing ability [57]. In particular, fiber Bragg grating (FBG) sensors have been very successful in measuring strain, temperature, and vibration in various applications [813]. Thus, they can also be used to detect leak vibro-acoustic signals of pipelines in inaccessible areas of WDNs.

The vibration in pipelines of a WDN includes both longitudinal waves propagating in the axial direction of the pipe and transverse waves propagating in the radial direction, which leads to the fluid-pipe coupled vibration [14, 15]. The basic forms of fluid-pipe coupled vibration are the breathing mode (n = 0) and bending mode (n = 1). Since most pipelines are buried and constrained, it is difficult to detect vibration in the bending mode. The breathing mode induces the expansion and contraction of the pipe surrounding the water stream because of the pressure change caused by the water flows. In addition, in the event of a leak, the fluid sound propagates along the pipe, and the leak signal exists in a low-frequency band [15]. The detection of leak signals using FBG sensors particularly measures the radial component of breathing mode.

In this paper, we present results from leak vibration measurements performed on a water distribution pilot plant. The water distribution pilot plant consists of four pipe types made of different materials with a total length of 270 m. The leak was simulated by directly drilling a leak hole on the side, and FBGs were used as vibration sensors to detect leak vibro-acoustic signals. The recorded leak signals were analyzed by fast Fourier transform (FFT) in real time. At a pressure of 1.8 bar and a flow rate of 25.51 m3/h, the experiments revealed a frequency difference in the leak signal depending on the type of pipeline and the size of the leak hole.

Ⅱ. EXPERIMENT SETUP

The experiments were conducted on a water distribution pilot plant with a length of 270 m developed in the smart water research center of the K-water Research Institute. The water distribution pilot plant consists of straight pipes with a maximum length of 6 m, elbows, flanges, pipe supports, pumps, valves, etc., as shown in Fig. 1, and their dimensions and fluidic parameters are listed in Table 1. Four pipe types are installed, including a cement mortar lining ductile cast iron pipe (DCIP), which is the main pipe type buried underground, a polyethylene pipe (PE) as a plastic pipe, a steel pipe (SP) with epoxy inner coating and polyethylene outer coating, and a 30-year-old ductile iron pipe (DIP). Each pipe has an average length of 70 m and diameter of 100 mm. For the water circulation system, directional flow from the water reservoir to the pipelines is engaged by pump-generated pressure, and after the completion of circulation, the flow returns to the water reservoir.

TABLE 1. Specification of water distribution pilot plant.

ParameterValue
Facility Area (m2)316
Pipe MaterialDCIP, PE, SP, DIP (old)
Total Length (m)270
Diameter (mm)100
Water Pressure<10 bar
Water Velocity (m/sec)0.07–2.0


Figure 1. Schematic of water distribution pilot plant. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.

To replicate pipe leaks, 1-, 2-, 3-, and 4-mm diameter leak holes were drilled into each surface of straight pipe segments in four monitored regions located in the middle of the pipeline (Fig. 1 and Fig. 2), and then tapping saddles were fastened as shown in Fig. 3(a). The tapping saddle can turn the water leak on and off using a valve [Fig. 3(b) and 3(d)]. Starting from one end of the pipe segment, four leak points were evenly spaced by approximately 50 cm (Fig. 2).

Figure 2. Fiber Bragg grating (FBG) sensor and leak points in monitored region.

Figure 3. Experimental layout: (a) leak simulator fastened with tapping saddle, (b) Leak hole, (c) FBG sensor bonded onto DCIP, (d) Water leak from 4 mm leak hole, and (e) FBG sensor interrogation system. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.

FBG sensors were used to detect vibro-acoustic signals in the four monitored regions. After removing foreign substances from the pipeline surface, FBG sensors were placed 1.2 m away from the starting point of the pipe segment [Fig. 2 and Fig. 3(c)] in each monitoring region and bonded with epoxy adhesive.

The distances from the FBG sensor to the 1-, 2-, 3-, and 4-mm leak points were 2.80, 3.30, 3.85, and 4.40 m, respectively. Four bare-type FBG sensors, with a reflectivity of 80%, an FWHM of 0.2 nm, Bragg wavelengths of 1550.37, 1555.05, 1560.78, and 1565.49 nm, respectively, were used in the experiment, as shown in Table 2. Fig. 3(e) depicts the FBG sensor system, which comprises a C-band erbium-doped fiber amplifier module with 40-nm (1530–1570 nm) 3-dB bandwidth and 17-dBm output power, an InGaAs photodiode array (PDA) module equipped with a volume phase grating and 512-px PDA, and an optical fiber circulator to demodulate the Bragg wavelength of the FBG sensors. The reflected Bragg wavelengths are fed to the InGaAs PDA through the circulator. Shifts in Bragg wavelength due to leak vibration can be measured using the PDA at a sampling rate of 3 kHz and analyzed by FFT.

TABLE 2. Monitored region and Bragg wavelength of fiber Bragg grating (FBG) sensors.

SensorsMonitored RegionBragg Wavelength (nm)
FBG 1DCIP1550.37
FBG 2PE1555.37
FBG 3SP1560.78
FBG 4DIP (old)1565.49

III. RESULTS

To verify the performance of FBG vibration sensors, an acoustic signal was applied to the monitored region of the DCIP using an acoustic speaker for the simulation of leak-induced vibration while the pump was turned off, as illustrated in Fig. 4. As shown in Fig. 5, acoustic signals of 100–1000 Hz were applied at intervals of 100 Hz 3.9 m away from the FBG sensor, and the resulting vibro-acoustic signals were measured using the FBG sensor interrogation system for FFT analysis. The results showed that the FBG vibration sensor system can effectively measure vibro-acoustic signals applied by the acoustic speaker.

Figure 4. Layout for frequency measurement of FBG sensor.

Figure 5. Preliminary test of frequency shift measurement depending on speaker-induced acoustic signals.

Fig. 6 shows FFT analysis results according to different leak sizes in the four pipe types. For comparison, the measurement of a no hole case (none) was included as well. Twenty experimental cases are listed in Table 3. Pressure and flow rate were set to 1.8 bar and 25.51 m3/h, respectively, in compliance with the general pressure of a WDN (1.5–7 bar or 1.53–7.1 kgf/cm2) designated by the Korean design standard [16]. In the case of no leak, vibro-acoustic frequencies of 342 Hz for DCIP, 357 Hz for PE, 364 Hz for SP, 371 Hz for DIP (old) were detected.

TABLE 3. Experimental cases.

Pipe TypeLeak Hole Size (mm)
DCIPnone; 1; 2; 3; 4
PEnone; 1; 2; 3; 4
SPnone; 1; 2; 3; 4
DIP (old)none; 1; 2; 3; 4


Figure 6. FFT results according to the leak size. (a) ductile cast iron pipe (DCIP), (b) polyethylene pipe (PE), (c) steel pipe (SP), (d) ductile iron pipe (DIP) (old).

When the leak size was increased to 1, 2, 3, and 4 mm, the peak frequencies at DCIP [Fig. 6(a)] were 384, 389, 395, and 394 Hz, respectively, at PE [Fig. 6(b)] were 390, 391, 395, and 397 Hz, respectively, and at SP [Fig. 6(c)] were 405, 410, 414, and 411 Hz, respectively, and at DIP (old) [Fig. 6(d)] were 392, 417, 411, and 414 Hz, respectively. As the leak size increased, it was confirmed that peak frequencies in all pipes increased as well by approximately 21–52 Hz compared to the case of no leak.

Fig. 7 summarizes the frequency shifts shown in Fig. 6, which ranged from 340 to 440 Hz due to the variation of the leak size. The peak frequency of all pipelines increased as the leak diameter increased, but it was difficult to distinguish the leak size. Frequency changes according to the leak diameter were approximately 10 Hz in DCIP, 6 Hz in PE, 9 Hz in SP, and 25 Hz in DIP (old). However, as soon as a leak occurred, the frequency in all pipes shifted significantly due to the pressure change. The shifts of peak frequency were 42 Hz in DCIP, 39 Hz in PE, 41 Hz in SP, and 21 Hz in DIP (old). It shows that frequency shifts can be used to detect leaks in pipelines.

Figure 7. Frequency shifts against the leak size.

IV. CONCLUSION

In this paper, leak measurements were performed on a water distribution pilot plant using FBG sensors that were installed on the pipeline surface and used to detect leak vibration signals at a sampling rate of 3-kHz. The leak was demonstrated using four pipe types and 1–4-mm diameter leak holes with tapping saddles on the surface of the pipelines. The frequency response of the leak signal was analyzed by FFT analysis in real time. From the experimental results, the frequency range of leak signals was approximately 340–440 Hz at a pressure of 1.8 bar and a flow rate of 25.51 m3/h. When a leak occurred, the peak frequency of all pipelines tended to increase, but it was difficult to distinguish the leak size. However, as soon as the leak occurred, the peak frequencies in all pipes shifted significantly by approximately 21–42 Hz compared to the no leak case, which can be used to detect a leak in pipelines.

Future work will focus on using experimental data in the fiber optic-distributed acoustic sensing system, measuring the trend of vibro-acoustic changes of the components of WDNs, and implementing field tests of old pipelines or specific areas of smart WDNs, where risks are expected.

DISCLOSURES

The authors declare no conflicts of interest.

DATA AVAILABILITY

Data underlying the results presented in this paper are not publicly available at the time of publication, which may be obtained from the authors upon reasonable request.

ACKNOWLEDGMENT

This research has been performed as Project No Open Innovation R&D (20-A-T-002) and supported by K-water.

FUNDING

Korea Water Resources Corporation (Open Innovation R&D 20-A-T-002).

Fig 1.

Figure 1.Schematic of water distribution pilot plant. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 2.

Figure 2.Fiber Bragg grating (FBG) sensor and leak points in monitored region.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 3.

Figure 3.Experimental layout: (a) leak simulator fastened with tapping saddle, (b) Leak hole, (c) FBG sensor bonded onto DCIP, (d) Water leak from 4 mm leak hole, and (e) FBG sensor interrogation system. DCIP, ductile cast iron pipe; PE, polyethylene pipe; SP, steel pipe; DIP, ductile iron pipe.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 4.

Figure 4.Layout for frequency measurement of FBG sensor.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 5.

Figure 5.Preliminary test of frequency shift measurement depending on speaker-induced acoustic signals.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 6.

Figure 6.FFT results according to the leak size. (a) ductile cast iron pipe (DCIP), (b) polyethylene pipe (PE), (c) steel pipe (SP), (d) ductile iron pipe (DIP) (old).
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

Fig 7.

Figure 7.Frequency shifts against the leak size.
Current Optics and Photonics 2022; 6: 137-142https://doi.org/10.3807/COPP.2022.6.2.137

TABLE 1 Specification of water distribution pilot plant

ParameterValue
Facility Area (m2)316
Pipe MaterialDCIP, PE, SP, DIP (old)
Total Length (m)270
Diameter (mm)100
Water Pressure<10 bar
Water Velocity (m/sec)0.07–2.0

TABLE 2 Monitored region and Bragg wavelength of fiber Bragg grating (FBG) sensors

SensorsMonitored RegionBragg Wavelength (nm)
FBG 1DCIP1550.37
FBG 2PE1555.37
FBG 3SP1560.78
FBG 4DIP (old)1565.49

TABLE 3 Experimental cases

Pipe TypeLeak Hole Size (mm)
DCIPnone; 1; 2; 3; 4
PEnone; 1; 2; 3; 4
SPnone; 1; 2; 3; 4
DIP (old)none; 1; 2; 3; 4

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