Research On Optical Measuring Methods Of Micro Bubbles Of Ship Wake

Ship wake is an inherent feature of a vessel left at sea, it is a underwater belt which is formed of a large number of bubbles. Wake is hard to eleminate, which provided information for detecting the presence of ships. Underwater ship wake bubble research progress today, most of the work is still confined to the laboratory simulation and analysis, optical measurement technology for measuring the real ship wake under marine environment is rare. Instruments can measureing are mostly acoustic device or SAR(Synthetic Aperture Radar) imaging equipment. These devices are difficult to measure internal morphology and parameters in the wake. The size of about 10 ~ 1000μm small bubbles can reflect the wake’s many features. So the research, development Ocean Optics equipment capable of measuring ship wake bubble curtain flow characteristic parameters is very important which can provide theoretical basis and the data for the study and detect ship wakes. In order to study and measure the real ship wake bubble curtain under marine environment, this paper developed an underwater optical measurement equipment, which is the first set of optical sea trials for a more complete measurement of wake, with large, Small Field two measurement capability. Offshore experiments show that the equipment can quickly and more accurately measure the ship wakes bubble curtain physical characteristic parameters(density, size, speed), and provide theory of reference and data support for the study of ship wake.1) Air bubbles spatial distribution inside the wake is difficult to obtain by conventional two-dimensional imaging, and spatial distribution of bubbles, especially the bubble space density of the wake is the most important parameter. To measure this parameter, this paper presents a laser slicing wake measurements method, witch collecting a group of consecutive wake-sectional slices through the laser to obtain spatial data wake. One of the key technologies of laser chips, optical sampling system,and scanning control are theoretical analysis and detailed design. Offshore experiments show that the laser scan slice method can collect to a maximum of 256cm3(100 mm × 40 mm × 64 ㎜) of wake interval data, reaching the sampling requirements for offshore measurements.2) For complex wake-sectional image data, proposed a bubbles particle identification method,constructing different types feature vectors of bubble particles, to classify a variety of imaging state bubbles particle and Identify image sequences wake section based on K-nearest neighbor learning algorithm.Measured results show that the method can successfully identify superposition bubbles,masked bubbles and incomplete imaging bubbles.while the conventional approach is difficult to identify such a complex image, the method has certain robustness. Density of complex imaging wake bubble curtain are calculated based on this method.3)10μm level bubble particles generated at most 3 × 3 projected pixels, grayscale region 3 × 3 is unable to distinguish with the suspended particles, or other interference.to solve this problem, this paper proposes a recognition method based on motion feature, first calculate the velocity vector field of image slice, and then based on the K-mean-means clustering algorithm to cluster velocity vector. Final cluster centroid is set for the identification basis. Measured results show that the method can identify vast majority of small bubbles particles which have identical behavior and calculate the average speed of the bubbles particles.4) For diffusion angle information of macro large field of wake turbulence, first proposed underwater visible light measurement method, first, by calculating the attenuation of light propagation in the water, establishing macro wake lighting methods and sampling methods. Secondly, there is a plurality of interference regions in the macroscopic wake image, in order to measure the change of diffusion angle with high reliability, we proposed a wake region extraction method based on form factor filtering merger Convex Hull smoothing edges dramatic ups and downs. Extracting wake region using image partition strategies to fit wake contour wiht line, the method achieve high reliability of automated extraction of macro-wake zone. Finally, conducted underwater offshore measurements experiments, the method statistics macro wake spread angle, the measurement value coincide with an assessment of the macro-diffusion angle in the current literature.