Design And Experimental Study On A Small-gap Measurement System Of Properties Of Seabed Sediments

Seafloor sediment acoustic properties research has important significance in economic construction and national defense. The main acoustic parameters of seabed sediment acoustics research include:the sound velocity, the acoustic attenuation. But the existing seabed sediment acoustics research was just to reflect the comprehensive effect of the whole sediment samples, and unable to study the acoustic properties of sediment in the micro-structure. So in order to satisfy the requirement of seabed sediment research in micro-structure, a multi-channels measurement system with the probes and complex programmable logic components based on former research, and the acoustic properties research of seabed sediment on small-gap was carried out, as well as the sound signal of the sediment sample on small-gap was obtained.The existing research of seabed sediment measurement system was introduced in this paper, including the situ measurement system and laboratory measurement system. The main acoustic properties of seabed sediment and the preparation of sediment samples were introduced as well. Moreover the calculation method of the sediment sound velocity and the acoustic attenuation was analyzed based on this experimental measurement principle.This system consisted of structure positioning subsystem and sampling measurement subsystem. The principle and function of the vertically movable module and horizontally movable module and the probe structure were introduced in this paper. The hardware platform of the measurement system was introduced through the hardware components of the sampling measurement subsystem. And the interface circuits were introduced in detail, included the ultrasonic signal transmitting module and the ultrasonic signal receiving module. Moreover the AD9850frequency control word program was written, and program flow charts of the each module were showed in the paper. The analog sound wave signal of the sediment samples was converted to14-bits signal and was stored in an external twin port RAM. The PC data reading and processing program was written by VB6.0, and the flow chart was showed in this paper.The time difference between two acoustic probes was obtained through the experimental measurements. In order to represent the acoustic properties of the sediment sample accurately, the error of the sound velocity and acoustic attenuation of the whole measurement system was checked. Based on the acoustic properties measurement system, the seabed sediment acoustic properties on small-gap measurement experiment was carried out using the two probes to be sensors. And analyzing the sound wave signals collected by the measurement system, mainly included sound velocity and acoustic attenuation. The influence of the experimental measurement results with the same measurement distance and different sampling rates was studied, and proved that fluctuations of sound velocity and acoustic attenuation were the same, based on the analysis comparison of two results measured by different sampling rates.The improving advice about the seabed sediment acoustic properties on small-gap measurement experiment was presented in this paper, combined with the problems found in the experimental measurement.