Research On B-mode Ultrasound Imaging Measurement Method For Sediment Transport Process

During sediment transport process,research on the measurements of sediment particles incipient movement,and suspended-load sediment concentration including its distribution,bed-load sand wave motion and river bed erosion and deposition has a vital theoretical and practical significance.At present,there is no feasible and reliable effective method to measure the sediment incipient velocity in river model experiment.And the measurements of suspended sediment concentration and sand wave surface bed basically belong to point measurements,which is impossible to directly obtain the real-time spatial distribution of suspended sediment concentration or the visualization and real-time dynamic monitor of sand wave topography(such as pulverized coals topography),and also the real-time monitor of sand wave motion under muddy water including moving sediment particles near the river bed.All of these have restricted the research of sediment movement law and the development of river model experiment measurement technique.Because the ultrasonic beam transmitted from B-mode ultrasound instrument has good penetration in sediment-laden flow and can realizes the real-time imaging of sediment transport process,this article directly uses B-mode ultrasound instrument to obtain the real-time imaging of sediment-laden flow and sand wave topography.We obtained a lot of B-mode ultrasound images of suspended-load particles,bed-load sediments and sand wave topographies under muddy or clear water in river model experiments.For the obtained ultrasound images,the statistical analysis of suspended sediment particles' imaging spots,we can get the suspended sediment concentration and its spatial distribution in the water.Through recognition and extraction of sand wave topography bed's imaging bright band,we can realize the real-time monitor,visualization measurement and 3D reconstruction of surface bed under muddy water.When sediment particle source is fixed and flow condition is under the control,we can obtain the incipient motion states of bed-load sediment particles under the effect of different water flows.After the statistical analysis on the number of moving sand particles and the imaging boundary of topographic surface at the same time during multiple frame images,we can realize the measuring analysis of sediment incipient motion and incipient velocity.The B-mode ultrasound imaging measurements and real-time dynamic analysis of suspended sediment concentration including its space distribution,sediment incipient velocity and sand wave topography during sediment transport process promote the development of sediment movement law and river model experiment measurement technique.For the B-mode ultrasound imaging measurement issues of suspended sediment concentration,sediment incipient velocity and sand wave topography during sediment transport process in river model experiment,we put forward some novel solutions and measuring methods.The main research results are summarized as follows:(1)For the statistical problems of suspended sediment particles' imaging spots in the B-mode ultrasound image,dissertation proposes a pixel labeling method based on morphological risk estimates.After image preprocessing,the method uses Bayesian risk estimation for sediment particles' imaging spots and topographic imaging bright band,and concludes the threshold of minimum cost for image binaryzation threshold segmentation,and then adopts a morphological filtering method and a pixel labeling method based on regional growth to realize the statistical analysis of the number of sediment imaging spots.This method can effectively solve the optimization problems of Speckle noise and sediment imaging spots adhesion or fold over the image.(2)For the identification and extraction of topographic bed's imaging bright band in B-mode ultrasound image,this dissertation proposes an adaptive tracking extraction method for the imaging bright band of underwater sand wave topographic bed,and uses a adaptive wavelet threshold denoising method based on contraction coefficients of wavelet domain.By using the imaging characteristics of bed imaging bright band,the method ignores the interferences of the Speckle noise and the other imaging spots,and just focuses on the imaging bright band of topographic bed.The method starts from the center of image where the imaging signal is relatively strong,and scans from up to down,and then gets one point of imaging band as the starting point in tracking.Lastly,it scans out to two sides of the starting point for the automatic tracking of imaging bright band.This method is fast,and has the advantage of strong adaptability.It implements the one-pixel-wide extraction of topographic boundary at once.This method solves the real-time monitor and on-line analysis of sand wave topographic bed under complex or muddy water flow conditions.(3)Based on the sediment incipient motion and imaging spots sudden addition phenomenon of moving particles near the bed surface in B-mode ultrasound image,dissertation proposes a method of measuring sediment incipient velocity based on the B-mode ultrasound imaging.Experimental results show there are same features in the image for the imaging signals of different sand materials and particle sizes,that is,the imaging spot concentration of sand particles near the bed is low when flow velocity is smaller than sediment incipient velocity,and the imaging spot concentration increases slowly with the increase of flow velocity.However,the imaging spot concentration is suddenly increased when the flow velocity is up to or bigger than the sediment incipient velocity,and the related curve of the imaging spot concentration happens to change hugely.According to these features,through multiple sets of water channel experiments with different flow sections,the imaging spot concentration curve and imaging area concentration curve changed with flow velocities are obtained,and their change rate curves are also analyzed.The extreme turning points of these curves are analyzed when the sand imaging spots are suddenly changed.The imaging particle and area concentrations both have a mutation process during the sediment incipient process.According to the mutation process,the sediment incipient movement is determined and its incipient velocity can be measured based on the corresponding flow velocity.Lastly,the measured sediment incipient velocities are verified by using the changed topographic bed and Prewitt corner detection method.(4)For the corresponding relationship problem of sediment imaging spots under different suspended sediment concentrations,the dissertation puts forward a novel method to measure suspended sediment concentration and its vertical distribution based on the B-mode ultrasound imaging.By analyzing the statistics of area concentration,gray concentration and energy concentration in the images under different suspended sediment concentration,the relationships between these statistical concentrations are established by calibration tests,and the imaging measurement of unknown suspended sediment concentration is realized in the sediment-laden flow.Meanwhile,according to the position distribution of suspended particles' imaging spots in the image,the spatial distribution analysis and hierarchical measurement along with the depth of sediment concentration is also realized.Calibration tests show this method is suitable for the imaging measurement of suspended sediment concentration with less than 5 ‰ or about 10 kg/m3 at present.This method has high sensitivity,good real-time and can monitor flow without disturbance.B-mode ultrasound imaging can real-time measure the dynamic changes of suspended sediment concentration and its vertical distribution in sediment-laden flow.(5)For the real-time monitor and visualization analysis problem of sand wave topographic bed under muddy water,dissertation puts forward a kind of visualization measurement and 3D reconstruction method for sand wave topography under muddy water flow by using B-mode ultrasound imaging technique.Based on the similarity and gradual change of topographies in consecutive fiames,this method automatically tracks topographic lines of river bed imaging bright band,and real-time monitors the change of bed boundary,and then goes on 3D model reconstruction.Calibration tests show that the visualization measurement and 3D reconstruction errors are not bigger than 1 mm for topographic bed.This method effectively eliminates the influence of moving sediment particles,and recreates the original sand wave topographic surface under muddy water flow.It realizes the real-time dynamic measurement of sand wave topographic bed and the statistical analysis of sand wave's peak,trough,wavelength and its moving speed in sediment-laden flow.This method provides an effective way to observe sand wave motion and the measurement of topography under muddy water during river model experiment.In brief,the application of B-mode ultrasound instrument and related imaging measurement methods in river model experiment has realized the sediment-laden flow imaging measurements of main motion features during the sediment transport process,that is,the real-time measurements of sediment incipient velocity,suspended sediment concentration including its space distribution,and the motion process of sand wave topography.It has a vital significance for the research of the interaction mechanism of sediment-laden flow,sediment transport law and river bed evolution law.Another,B-mode ultrasound imaging method has realized the visualization measurements of sediment-laden flow and sand wave motion process.It brings traditional complex point measurement research into intuitive and fast image measurement research with linear,square and cubic styles.This method opens a novel approach and method for the measurement problems of muddy water river model experiment.