{'fraction_non_alphanumeric': 0.018274111675126905, 'fraction_numerical': 0.0010152284263959391, 'mean_word_length': 5.358064516129033, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
Numerical and experimental study on leakage detection for buried gas pipelines based on distributed optical fiber acoustic wave

Buried natural gas pipeline leakage can cause severe environmental pollution and human casualties. The currently used fiber optic temperature sensors cannot detect pipeline leakage in all directions, and there are monitoring blind spots. Besides, there is a lack of field tests and verification of the acoustic characteristics caused by leakage. In this work, a sound wave attenuation model considering gas flow in viscous porous media is established based on the Φ-optical time-domain reflectometry (Φ-OTDR) principle, combined with fluid dynamics and acoustic wave propagation mode in porous media (soil). The attenuation characteristics of acoustic wave propagation in soil are studied by varying the leakage hole size and leakage pressure. It is found that the acoustic source of buried natural gas pipeline leakage belongs to broadband noise. The acoustic signals detected by optical fiber acoustic sensors are vary with different leakage holes and leakage pressures. In particular, the leaked acoustic wave’s energy is prominent in the low-frequency band of 15 kHz, and the sound pressure level (SPL) oscillates and attenuates with the increase in frequency. With the increase in the transmission distance, the amplitude of the pipeline leakage signal gradually attenuates. Eventually, the acoustic wave decays to the point where the fiber-optic acoustic sensor cannot detect it. The optimum frequency of acoustic wave propagation in soil is obtained through experimental research. The propagation characteristics of acoustic waves in the soil are not a fixed value. The simulation results are in good agreement with the experimental results, indicating that the SPL in the low-frequency band is significant for pipeline leakage monitoring. The above research results can provide valuable guidance for field optical fiber installation.