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In synthetic aperture sonar (SAS) image, the underwater shipwreck targets are often buried by sediment or badly damaged. Only a part of the characteristics of artificial objects is retained. In this paper, firstly, based on the analysis of the ocean buried background, the Meanshift filtering is used to smooth the original image and convert the color image into binary one. Secondly, the residual contour of artificial target is extracted through the modified Canny edge detection algorithm. Thirdly, the Region Growing method is taken to remove the discrete interference and keep the intact edge of the line. Consideration with the principle of line alignment, the contours of shipwreck targets are gradually connected and aggregated. Finally, a large amount of measured practical SAS images are tested. The experimental results verified that the proposed algorithm can accurately detect the shipwreck target based on residual contour information, meanwhile with an acceptable timeliness for large size sonar image data.

This paper presents a statistical model updating technique for damage detection of underwater pipeline systems via vibration measurements. To verify the reliability of the method, laboratory tests of a scaled pipeline model were carried out in a towing tank. The model includes a plastic pipe and some removable springs which are designed and fabricated to link the pipe and the steel base to simulate the bedding conditions. Different damage scenarios, in terms of location and severity of scouring under the pipe, were simulated by removing one or several springs. The natural frequencies, damping ratios and mode shapes of the pipeline system were extracted from the measured vibrations using a stochastic subspace identification technique. Both the numerical and the experimental results show that the method is effective and reliable in identifying the underwater pipeline bedding conditions and the damage in the pipe structure.

India is rich in its heritage and culture. It has many historical monuments and temples where the walls are made of inscribed stones and rocks. The stone inscriptions play a vital role in portraying about the ancient incidents. Hence, the digitization of these stone inscriptions is necessary and contributes much for the epigraphers. Recently, the digitizing of these inscriptions began with the binarization process of stone inscriptions. This process mainly depends on the thresholding technique. In this paper, the binarization of terrestrial and underwater stone inscription images is preceded by a contrast enhancement and succeeded by edge-based filtering that minimizes noise and fine points the edges. A new method called modified bi-level thresholding (MBET) algorithm is proposed and compared with various existing thresholding algorithms namely Otsu method, Niblack method, Sauvola method, Bernsen method and Fuzzy C means method. The obtained results are evaluated with the performance metrics such as peak signal-to-noise ratio (PSNR) and standard deviation (SD). It is observed that the proposed method has an improvement of 49% and 39%, respectively, on an average by the metrics considered.

A reactor is a pressurized core safety instrument in a NPP(Nuclear Power Plant). It is made of carbon steel and its inner surface is covered with stainless steel. Its body consists of three cylinders and they are welded to each other. There are several holes for inlets and outlets in the reactor body. The welding areas are vulnerable points for a reactor. The inspection of a rector welding areas is one of the most important maintenance procedures during a NPP overhaul period. We developed a underwater reactor welding area UT(Ultra-sonic Test) inspection system for a pre-service. The main components of the inspection system are an underwater inspection robot, a laser positioner, a UT analysis system and a main control system. We executed an underwater UT inspection for the Ulchin unit 6 at Doosan Heavy Industries with the developed inspection system.

This paper introduces a study of a concept of flexible crawling mechanism to design an industrial underwater cleaning robot, which is evaluated from the viewpoint of the capability to work underwater, scanning the desired surface, and bearing the reactions. This can be used as a robotic application in underwater surface cleaning and maintenance. In this study we focused on realizing the adhesion on the surface in stationary and in motion, bearing reactions, enabling the needed locomotion types for scanning, and achieving the stability in different situations on the surface.