| As one of the five major transportation modes,pipelines are an important means of energy transportation.Leak in buried gas pipelines poses significant safety hazards and can even lead to major accidents.The acoustic-based detection and localization method for pipeline leak has been widely researched and applied due to its advantages of high accuracy,real-time capability,and low false alarm rate.However,the calculation of jet flow field induced by buried gas pipeline leak does not consider the coupling mechanism between jet flow and soil,which hinders the accurate determination of flow field parameters and restricts the study on the generation mechanism and acoustic field characterristics of jet flow aeroacoustics.The existing large-scale detection and localization technology based on the acoustic method is limited in accuracy and lacks anti-interference capabilities,failing to effectively utilize spatial acoustic field characteristics for sub-meter level localization of underground leaks within the leak area.To address these issues,this study focused on the steel pipe covered with soil outdoors and investigated the precise localization method for buried gas pipe leak using the characteristics of spatial acoustic field.Based on the analysis of computational fluid dynamics(CFD)coupled with discrete element method(DEM)for the leak jet and soil,the leak jet flow field and acoustic field under gas-solid coupling effect were modeled.The flow field characteristics and aeroacoustic source generation mechanisms were revealed.Sensor array technology was introduced for leak-induced acoustic field imaging.According to the spatial distribution characteristics of leak-induced acoustic field,the leak acoustic source was accurately located in sub-meter level by special array topologies and innovative algorithms.The main investigations and conclusions are as follows.(1)The governing equations of fluid were used to describe the gas flow inside and outside the pipe as well as in the area of soil.The particle motion equations were employed to describe the movement of soil particles,and a coupled CFD-DEM analysis model for buried gas pipe leak was constructed.Numerical simulations clarify that the soil within the leak jet area transitioned from a compact state to a dry and loose-particle state(the movement speed of particle reached 1 m/s),while the external soil remained compact and stationary.Loose soil particles can only partially impede the development of leak jets,which still remain supersonic flows.In the case of 1.0-MPa internal pressure and 0.3 porosity,the maximum flow speed was 992 m/s.This provides conditions for the generation of aeroacoustics.(2)Based on the flow field parameters,the numerical analysis of acoustic field was conducted,which clarified that the turbulent fluctuations caused by the high-speed flow of the leak jet generated the jet noise source,belonging to a quadrupole acoustic source.The low-speed laminar flow near the leak hole wall had higher turbulence kinetic energy and produced boundary layer noise sources with higher power levels,belonging to dipole acoustic sources.The frequency response of leak-induced pipe wall vibration signal was concentrated in the high-frequency band of 0.94 – 24.8 k Hz,while that of the ground vibration signal was concentrated in the mid-to low-frequency range of 0.25 – 0.8 k Hz.Experimental results show that the proposed super-resolution imaging function was able to accurately image the leak acoustic source in pipe wall cylinder and soil space,which verified the consistency of the locations of acoustic source and leak hole and proved the feasibility of locating the leak-induced acoustic source using array techniques.Different porosities(proportion of solid phase of soil)result in changes in static pressure on pipe walls and attenuation characteristics of wave propagation through soil media,thus affecting leak-induced acoustic source imaging.Under an internal pressure of 1 MPa,as porosity increased from 0.3 to 0.5,maximum acoustic power levels of imaging for pipe wall as well as P1 and S waves through soil increased by 14 d B,20 d B,and 19 d B respectively.(3)A large-scale pipeline localization method based on a linear array along the pipe wall was proposed.The speed at which the vibroacoustic wave propagating along the pipe wall and the location of the leak-induced acoustic source were estimated step by step using an M – 1 element subarray and its corresponding M-element array,respectively.This approach improved the localization accuracy while achieving joint step-by-step estimation of both parameters.Experimental results showed that compared to the classical cross-correlation methods,the step-by-step method reduced localization errors by 94.4%and required 50% fewer sensors than joint estimation methods,with a computation time reduction of over 90%.Localization experiments in long-distance circular pipeline demonstrated that within different localization ranges,the error rate of the step-by-step method remained in the range of 0.21% to 0.24%,providing a relatively accurate aera of the leak.(4)To compensate for insufficient accurate localization of buried leaks within a specific area,a joint leak position and wave speed estimation method based on nonuniform planar arrays was proposed.By utilizing large-and small-aperture planar arrays installed on the ground in leak areas,relationships between direction of arrival(DOA)of far-field source and wave-speed were solved,achieving two-dimensional spatial spectrum estimation for wave-speed and near-field source distance.Ultimately,buried multi-leak localization was efficiently and accurately(sub-meter level)achieved.Experimental results showed that large-aperture arrays derived from expanding uniform L-shaped array had maximum aperture and optimal performance.With a signal-to-noise ratio(SNR)of30 d B,localization errors for buried leaks within an experimental range(2 m × 2 m × 1.3m)were proved below 0.02 m.Figure [96] Table [13] Reference [164]... |
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