Vibration Monitoring in Underground Pipeline Systems Using Fiber Bragg Grating Sensors

Abstract

Underground pipelines are vital to urban society, but are susceptible to vibration, strain from soil displacement, corrosion and temperature fluctuations. Electrical sensors face several challenges, including sensitivity to electromagnetic interference (EMI), lack of distributed sensing capability and stability in the underground environment. We demonstrate a Fiber Bragg Grating (FBG) based structural health monitoring (SHM) system in underground pipelines to monitor vibration.The system integrates three simulation software packages: COMSOL Multiphysics (finite-element modelling of structures), OptiSystem (optical sensor modelling) and MATLAB (frequency-domain signal processing). The strain for FBG sensor design is calculated from COMSOL’s Von Mises stress. OptiSystem modelling is used to evaluate the Bragg wavelength shift with strain (01500 µ?) and temperature (0-180 ?C). The MATLAB Fast Fourier Transform (FFT) is utilised to analyse vibration with combined FBG sensors. The system has strain sensitivity of 1.0-1.2 pm/µ?, temperature sensitivity of 14.3 pm/?C, grating length of 10-15 mm and vibration frequency of 10 Hz. This approach provides a scalable, EMI-proof and sensitive system for smart cities, smart maintenance and real-time fault detection in oil and gas, metro and utility pipelines.

Introduction

The rapid expansion of underground infrastructure such as oil and gas pipelines, water networks, sewer systems, and metro tunnels has increased the need for reliable structural health monitoring (SHM). These structures experience complex dynamic loads including traffic vibrations, earthquakes, soil pressure, settlement, and thermal expansion, which can cause fatigue cracks, corrosion, wall thinning, and structural failures. Traditional electrical sensors suffer from limitations such as electromagnetic interference, corrosion damage, signal loss, and limited point-based monitoring capability.

This research proposes an integrated Fiber Bragg Grating (FBG)-based SHM system for real-time monitoring of underground pipelines by combining COMSOL Multiphysics, OptiSystem, and MATLAB. FBG sensors measure strain and temperature changes through Bragg wavelength shifts, providing high sensitivity, immunity to electromagnetic interference, and suitability for harsh underground environments.

The literature review highlights that FBG sensors have been successfully applied in civil, geotechnical, and industrial monitoring due to their ability to measure multiple parameters such as strain, vibration, pressure, temperature, and corrosion effects. However, existing systems often lack an integrated framework combining structural simulation, optical sensing, and signal processing.

The proposed methodology consists of five stages:

1. Structural Modeling (COMSOL): A 3D finite element model of a buried pipeline is created to analyze stress distribution, soil interaction, and corrosion effects.
2. Stress-to-Strain Conversion: Mechanical stress is converted into strain values for FBG sensing.
3. Optical Simulation (OptiSystem): Strain and temperature changes are applied to FBG sensors to calculate wavelength shifts.
4. FBG Optimization: Grating length and refractive index modulation are optimized to improve reflectivity, signal-to-noise ratio (SNR), and sensitivity.
5. Signal Processing (MATLAB): Vibration signals are analyzed using filtering and FFT techniques.

Simulation results showed that corrosion significantly increases structural stress. At a 4 mm displacement, the pipeline defect region experienced stress above 800 MPa, indicating severe mechanical degradation. Over a 20-year period, corrosion depth approximately doubled and stress concentration increased by around 45%, confirming the need for continuous monitoring.

FBG sensor optimization showed that a grating length of 10–15 mm and refractive index modulation of approximately 10?? provided the best performance. The optimized 15 mm FBG achieved:

• Reflectivity: 69%
• Signal-to-noise ratio: 98.4 dB
• Narrow spectral width: 35 pm

Strain sensing experiments demonstrated a nearly linear relationship between applied strain and Bragg wavelength shift, with sensitivity around 1.2 pm/µε. Temperature analysis showed stable performance with sensitivity of 14.3 pm/°C over a wide temperature range.

Conclusion

This paper presents and assesses an integrated FBG-based SHM system for vibration monitoring of underground pipeline infrastructure, which integrates COMSOL Multiphysics, OptiSystem and MATLAB within a physically consistent analytical framework. The framework’s performance is validated by key results: strain sensitivity 1.0-1.2pm/µ?, temperatureNovelty Statement: The key contribution of this study lies in the first simultaneous use of three different simulation software (COMSOL Multiphysics, OptiSystem, and MATLAB) in one physically continuous framework for the vibration monitoring of underground pipelines. Rather than focusing on structural analysis, optical simulation, or signal processing as discrete tasks as was done in previous papers, this work provides a quantitative physical link from COMSOL-calculated von Mises stress, to Hooke’s Law strain, to OptiSystem-simulated Bragg wavelength shift, to MATLAB FFT vibration frequency. The comprehensive grating length study offering practical design insight (optimal: 10-15mm), and the successful temperature compensation technique to pinpoint a 10Hz vibration signature from a composite signal are novel contributions to the FBG-based SHM techniques.

References

[1] C. V. N. Bhaskar, S. Pal, and P. K. Pattnaik, “Recent advancements in fiber Bragg gratings based temperature and strain measurement,” Results in Optics, vol. 5, p. 100130, 2021. [2] A. Tripathy, “Evaluation of an optical fiber Bragg grating as a strain sensor,” in Proc. VSPICE Conf., 2020. [3] A. S. More, P. S. Lad, S. R. Krishnan, and S. R. Bhosale, “Performance analysis of strain sensor based on fiber Bragg grating,” ITM Web of Conferences, vol. 32, p. 03010, 2020. [4] X. Qiao, Z. Shao, W. Bao, and Q. Rong, “Fiber Bragg grating sensors for the oil industry,” Sensors, vol. 17, no. 3, p. 429, 2017. [5] M. I. M. Razi, M. R. C. Beson, S. N. Azemi, and S. A. Aljunid, “FBG sensor strain performance analysis using OptiSystem software tools,” Indonesian J. Elect. Eng. Comput. Sci., vol. 14, no. 2, pp. 564–572, 2019. [6] IANS, “Gas leak from ONGC pipeline in Andhra’s Kakinada,” The Economic Times Energy World, Aug. 2025. [7] “Industrial pipeline risk reports,” Global Times, 2019. [Online]. Available: https://www.globaltimes.cn/content/827035.shtml [8] W. Chalgham, K.-Y. Wu, and A. Mosleh, “External corrosion modeling for an underground natural gas pipeline using COMSOL Multiphysics,” in Proc. COMSOL Conf., Boston, 2019. [9] A. D. Kersey et al., “Fiber grating sensors,” J. Lightw. Technol., vol. 15, no. 8, pp. 1442–1463, 1997. [10] R. Kashyap, Fiber Bragg Gratings, 2nd ed. Academic Press, 2010. [11] B. Lee, “Review of the present status of optical fiber sensors,” Opt. Fiber Technol., vol. 9, no. 2, pp. 57–79, 2003. [12] Technica Optical Components, “T99 High Strength FBG Sensor Datasheet,” Atlanta, GA, USA, 2023.

Copyright

Copyright © 2026 Prof. Santosh Jagtap, Akansha Tandale, Ayush Babar, Ayush Thakur, Varsha Venkataraman. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.