The Research Of B-Ultrasonic Imaging Technique For2-D Flow Field With Sandiness

The research on the river model experiment has been restricted by sandness underwater two-dimensional flow field imaging measurement, the existing measuring technique based on the surface flow field of the optical principle and laser CCD imaging2-D profiles flow field imaging is not suitable for sandness underwater flow measurement. This paper presents a method based on the principle of B-Ultrasonic scanning for2-D measurement and imaging techniques under the condition of the sandness flow, abbreviated as UPIV (Ultrasonic Particle Image Velocimetry) method. The method applies ultrasonic linear array transducer to rapidly scan under the water to obtain the two-dimensional sand moving pictures. Then two-dimensional flow velocity information can be collected, and latter build up a two-dimensional flow field through the analysis of correlative maching of adjoining frames image. This method can real-time display flow and sediment movement of flow, obtain sandness movement of fine structure. It also helps to the study for the interaction mechanism of the sediment silting-up and evolution rules. This method has important application value.In this paper, digital image processing technique strongly supports B-ultrasonic imaging technology application in river model underwater flow measurement system. With this application, we systematically research the principle and structure of the UPIV system, ultrasonic particle image denoising and enhancement and the flow field reconstruction algorithm. A lot of experimental data is collected and the image analysis and process is completed. After the analysis of the main algorithm researched in the paper, the main conclusions and results are as follows:1. The B-ultrasonic imaging method is taked to measure underwater flow field for river model, and a set of underwater sandness flow field measurement and analysis system is build up. In the paper all the algorithm is completed through VC programming.2. Presents a new algorithm for reconstructing velocity field-second searching cross-correlation method. This method can search out all the estimated position of each diagnosis window with the FHT fast calculation advantage. Then taking the accurate advantages of block matching method to proceed the second correlation calculation. Based on the above mentioned, not only accuracy can be reached, but also time can be saved a lot. 3. For underwater particle number is sparse, and the sparse distribution of flow field, this paper presents the method of particle trajectories, taking the related technologies, by tracking each particle or particle swarm matching trajectory, get each particle or particle swarm moved displacement, thereby improving the flow measurement accuracy.4. The wavelet multiresolution matching algorithm applied to the velocity field reconstruction and take Mallat algorithms narrow diagnosis area for matching estimate, then precisely match at the bottom. This method effectively reduces the matching searching points and of calculations, and improve the accuracy of measurement.5. Taking adaptive weighted median filter, logarithmic transform method, wavelet soft threshold shrinkage method, taking the same speckle noise filter histogram equalization techniques to improve such image enhancement of original particle image clarity, make it easier for computing velocity field. Taking iterative method and the method of OTSU image threshold segmentation algorithm, it is well prepared for particle trajectories research.6. Presents a vertical center flow field calculation method, continuous tracking the given center area of the frame images, which defines the direction of movement particle synthesis, eliminate errors and displacement vector, gives a period of the particle movement speed and direction, true to satisfy the river model to study the flow field of underwater.7. In Fixed bed model experiments on the Yangtze river model the Jingsha section, the sandness underwater flow field of measurement and analysis system established in the paper, was taked for different flow time respectively, different section of the underwater flow field measurement and analysis, the first time the sandness underwater flow measurement was realized.