A Preliminary Study On The Suitability Of A New Ultrasonic Sediment Concentration And A Graded Measuring Probe

The study of sediment movement in natural rivers is not only related to the characteristics of sediment-carrying flow movement,but also of great significance to the water and sediment transport,river evolution,bank management,ecological protection of estuaries and rivers,soil and water conservation,prevention and control of debris flow.The sediment movement in natural rivers is very complicated.On the one hand,under the influence of water flow,the sediment movement makes the bed surface movable,and the sediment concentration in the water body distributes according to a certain law on the vertical line.On the other hand,water flow interacts with sediment,and sediment movement in turn affects flow structure.Therefore,it is important to get accurate measurement of sediment concentration and particle size distribution in rivers and estuaries,which puts forward new requirements in the field of hydraulic measurement science.Because there is no equipment that can accurately measure sediment parameters online in real time,and there are still many limitations in the existing sediment flow measuring technology.In this paper,based on a self-developed ultrasonic probe,the acoustic characteristics of sediment were studied,and the measurement performance and applicability of the probe were studied.Technical aspects include:(1)the ultrasonic probe is made of a new piezoelectric composite wafer and a rectifying block developed by GE to optimize the probe structure,reduce the signal-to-noise ratio and reduce the sound loss caused by sound wave propagation in the medium,(2)high frequency(5MHz)ultrasonic emission technology can not only measure very fine particles,but also effectively compensate the acoustic signal loss under high concentration,so that it has better measurement capability and is suitable for rivers with high sediment concentration,(3)through the gigabit Ethernet interface to realize the parameter setting and operation control of each probe,and ensure the correct reception and analysis of the massive data from the high-speed transmission of gigabit Ethernet interface,so as to achieve the purpose of real-time measurement.In this paper,three different groups of grading of natural sand and one group of plastic model sand are chosen for experiment,mixture of known concentration,water samples of sand mixture,concentration increases from 0.02kg/m~3 to 12kg/m~3,provide a stable concentration field using the electromagnetic stirrer,acoustic scattering signal is collected for each sample,compared to the experimental results of model sand at the same time,the difference between the acoustic characteristic analysis of different materials.·Independently wrote MATLAB GUI user interface to process the echo signal,and studied the relationship between scattered sound intensity and concentration;through data analysis,the measuring ability and stability of the probe are studied.In this paper,through the orthogonal experiment,found that the sediment concentration and distribution of measurement there is close relationship between,the following conclusions:(1)through the piezoelectric materials and the common chip,the acoustic measuring probe has better performance,the current 5MHZ concentration of high frequency ultrasound to up to 12kg/m~3 of water containing sand for good measure,waveform and spectrum graph there was no obvious amplitude decrease;(2)As the concentration increases,the sound intensity also increases.The relationship between sediment concentration and scattered signals is a power exponent function,and an acoustic model suitable for this probe is established by function fitting,(3)Sediment level paired concentration measurement has a great influence.The coarser the sediment particles are,the stronger the scattered sound is.On the contrary,the finer the sediment particles are,the smaller the scattered sound is.(4)The spectrum diagram shows that the thinner the composition of sediment particles is,the gentler the shape of the spectrum diagram is,and the thicker the composition of sediment particles is,the steeper the shape of the spectrum diagram is.(5)There are differences between the acoustic characteristics of model sand and natural sand,which are reflected in the exponential term of the acoustic model;(6)The measurement results of the probe are not affected by the length of sampling time,and the measurement results have good stability.The standard deviation of each group is less than 5%,meeting the specified requirements.