Simulation Of Ultrasonic Detection Of Submarine Gas Hydrate

In order to realize the accurate and efficient unmanned mining operation of the underwater mining vehicle,it is necessary to carry out real-time detection and identification during the mining process,and to judge the mining value of the hydrate.Based on the National Natural Science Foundation of China project "Research on the Hydraulic Transport Mechanism and System Design Method of Submarine Gas Hydrate Scissor-suction Mining",this paper established an acoustic model of shallow hydrate deposit which is based on the theory of two-phase porous media,and the ultrasonic detection technology is studied through simulation analysis and experimental analysis.The main research contents of the paper are as follows:Based on the theory of two-phase porous media,a model of hydrate ore seam on the shallow seafloor was established by using the acoustic simulation software.Based on the model,the influence characteristics of sediment location,ultrasonic emission parameters and sediment properties on echo reception were explored.The results show that when the ultrasonic incident angle is between 0°and 40°,the absorption coefficient of the mineral layer is the largest,and when the incident angle is greater than 60°,the absorption coefficient of the mineral layer is the smallest,and the echo is not available.The echo signal is mainly affected by the properties of the surface substrate,and it is easier for the sound wave to penetrate the substrate with high porosity and small pore size,and to reach the under-layer.The ultrasonic echo signal processing method in the seabed reverberation environment is discussed and analyzed.By studying the effect in processing the simulated seabed noisy echo signal through moving average method,coarse error method and filter method,it’s found that the IIR elliptic band-pass filter works best in dealing with noisy signals,while gross error method is not suitable.Aiming at the problem of grade identification of shallow seabed hydrate ore seam,a method based on cross-correlation is proposed.It can effectively distinguish the minerals with different grades by extracting the cross-correlation coefficient between pure hydrate sample and the other samples with varied grades.It also improves the reliability and accuracy of distinguishing samples with different grades by extracting the cross-correlation coefficient vector.When the cross-correlation coefficient threshold is set to 0.75,samples with hydrate mass fraction of more than 40% can be distinguished.Providing a theoretical support and technical reserve for the design and application of the ultrasonic detection system of natural gas hydrate as well.