Research On Measurement Technology Of Underwater Gas Emission Based On Acoustic Characteristics Of Self-generated Bubbles

Underwater gas escape phenomena are common in nature and industrial processes,such as submarine pipeline leakage,carbon storage failure,subsea cold spring detection,and bubble tower mass transfer and heat transfer.Accurate measurement of emissions has important scientific significance and application value for key fields such as energy security,environmental science,and chemical industry.Among the many methods,the bubble acoustic method uses the acoustic signal generated by the bubble oscillation to realize the measurement through the mapping relationship between the signal feature and the volume.It has the advantages of high precision and easy maintenance and has become a research hotspot in related fields.Aiming at the problem of low signal-tonoise ratio and continuous overlap during underwater high-speed gas escaping,the underwater gas escaping measurement technology based on bubble acoustics has been studied from theoretical modeling,algorithm research,and experimental verification.The main work includes:An underwater gas escape model was established and the sound wave propagation characteristics were studied.The COMSOL finite element simulation software was used to simulate the underwater gas escape process and the pressure disturbance caused by the vibration of the bubble wall,and the sound signal generation mechanism was clarified.The emulation signal is used to analyze the key and difficult points of the leakage measurement,which lays the foundation for the subsequent algorithm design.A high-speed gas escape measurement algorithm under the condition of low signal-to-noise ratio is proposed,which realizes the recognition of bubble volume oscillation mode through the preprocessing of the complete total empirical mode decomposition(CEEMD)method.The continuous bubbles are segmented through the normalized amplitude square to achieve high-precision measurement of volume inversion.The simulation signal is used to verify the leakage measurement,anti-noise performance and continuous bubble segmentation performance of the algorithm,and it has achieved good results.A set of gas escape measurement platform under laboratory conditions was built,and experiments were carried out under constant speed and variable speed gas escape conditions.The results show that the measurement error is within 3% for small constant-rate escapes within 100 m L/min;the measurement error is within 8% for higher escapes of 100-1000 m L/min.For 500 m L/5s variable speed gas escape,the measurement error is less than 4%.A set of fixed water measurement prototypes were developed,and software and hardware systems were designed based on FPGA and MATLAB to measure the amount of underwater gas escape.The test results in the lake water show that the measurement of the escaping volume is greatly affected by the underwater disturbance noise near the bubble generation,and less affected by the surface noise.The measurement platform built can perform accurate measurement within the effective range of 4 meters,and the measurement error is within 10%.