Abstract:Icing on transmission lines might lead to ice flashovers of insulators, collapse of towers, tripping faults of transmission lines, and other accidents. Shed spacing and shed overhang of insulators are clues for evaluating the probability of ice flashover. This paper researches imageprocessing methods for the natural icing of in-service glass insulators. Calculation methods of graphical shed spacing and graphical shed overhang are proposed via recognizing the convexity defects of the contours of an icing insulator string based on the GrabCut segmentation algorithm. The experiments are carried out with image data from our climatic chamber and the China Southern Power Grid Disaster (Icing) Warning System of Transmission Lines. The results show that the graphical shed overhang of insulators show evident change due to icing. This method can recognize the most serious icing conditions where the insulator sheds are completely bridged. Also, it can detect bridging positions including the left side, right side, or both sides of the insulator strings in the images.
The global stability of high arch dam is one of the key problems in the safety study of arch dams, but no feasible method with theoretical basis is available. In this paper, based on the stability theory of mechanical system, it is demonstrated that the global failure of high arch dams belongs to a physical instability starting from local strength failure, which is the extreme point instability according to the characteristics of load-displacement curve obtained from the failure process of dam-foundation system. So the global failure of dam-foundation system should be studied with the stability theory of mechanical system. It is also pointed out that the current stability analysis methods used in engineering are consistent with the stability theory, but not established according to the mechanical system stability theory directly. A perfect method can be obtained through the study of physical disturbance equations.
high arch dam, global stability, physical instability, extreme point instability
Citation:Ren Q W, Li Q, Jiang Y Z, et al. Theory and methods of global stability analysis for high arch dam.
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