Research On Measurement Method Of Large Turbidity Based On Ultrasonic Attenuation And Implementation Of Measurement System

Nowadays,human beings are no longer satisfied with the exploitation of terrestrial resources.With the advancement of technology,submarine polymetallic nodule minerals have entered the experimental mining stage from the investigation and research stage,in order to provide technical basis for future commercial exploitation,including mining impact to the seabed environment.The environmental impact caused by disturbance should be assessed,so mining disturbance environmental impact monitoring is very important.Submarine manganese nodules mining disturbs the marine environment,causing sediment to levitation and changing seafloor environmental parameters.The most intuitive effect is the change of turbidity value,even reaching the level of turbidity.Monitoring the change of seafloor turbidity value to assess the impact of submarine manganese nodules mining to ecosystem is of great significance.The requirements of seafloor turbidity monitoring have been analyzed in this paper,based on the shortcomings of traditional optical turbidity measurement,poor anti-interference ability and high cost,a method for measuring turbidity values by ultrasonic attenuation is proposed,which is used to achieve large turbidity,self-cleaning and real-time measurement of seabed water.The theoretical model of ultrasonic attenuation is studied.The theoretical parameters of the physical attenuation parameters and three acoustic attenuation models are used to establish the relationship between ultrasonic attenuation and frequency,attenuation and particle concentration.Because the mining machine disturbance causes the seabed sediment to have a single source of suspension,the EACH sound attenuation model can be used to design the monitoring method for the variation of the suspended matter concentration in the sea during the actual mining disturbance.The ultrasonic frequency range is below 2MHz.Based on the theoretical analysis results,an experimental system for measuring the turbidity value of the solid-liquid mixture using ultrasonic attenuation was established.Based on the NI virtual instrument platform,the ultrasonic transducer was selected,the excitation signal transmitting module and the ultrasonic signal processing module were designed.The virtual instrument program was developed and the measured object model was designed.Through the combination of software and hardware,the system construction using ultrasonic attenuation turbidity value is completed,and the functions of ultrasonic signal generation,ultrasonic signal acquisition,signal processing and sound attenuation calculation are realized.The ultrasonic frequency selected for the experiment is determined,and the center distance of the transmitting and receiving probe is determined according to the sound propagation characteristics.Based on the experimental design of the experimental system,the sediment was selected as the experimental object according to the characteristics of the seabed sediments in the polymetallic nodule mining area.The variation of the ultrasonic sound attenuation was studied by controlling the change of sediment concentration.Acoustic attenuation values and concentration models at three frequencies of 37 kHz,700 kHz and 1.5MHz were established.The XZ-0101 optical turbidimeter was used to test and establish a particle concentration and turbidity model,which are highly correlated in the 2000 NTU optical turbidity range.Finally,the relationship between the ultrasonic attenuation coefficient and the turbidity value is obtained.According to the model,the measurement range of the turbidity value at different ultrasonic frequencies is calculated to be greater than 5000 NTU,which proves that the ultrasonic attenuation method can be used to monitor the mining disturbance.