Explosion Damage Identification Method Of Concrete Dams Using Video Measurement

With the continuous development of dam construction technology worldwide and the urgent need of the whole society for green energy,a large number of 100-300 m high dams have been built or are under construction.These dams have high water level and large reservoir capacity.Considering the political and economic benefits and strategic position of the dam,it has become a key target in modern military confrontation such as war,terrorist attacks,etc.The possible ways of dam attacking are underwater explosion,air blast and direct hitting the dam body,among which underwater explosion is the most complex and common.Under the impact load of underwater explosion,the dam may have different failure modes,such as explosion pitting,overall tension,collapse and slip.It is difficult to identify and evaluate the underwater damage only by conventional methods.Therefore,the rapid and accurate identification of underwater explosion damage of dams has important guiding significance for rescue and disaster relief under emergency conditions of dams.It is of great significance to ensure the overall stability of the structure,the property and personal safety of downstream people.It is also a frontier key issue that must be solved in the safety management of water conservancy projects in China.In this paper,a video extraction method of modal parameters suitable for dam structures is proposed.The dynamic response and damage characteristics of the gravity dam and arch-gravity dam under the action of underwater contact explosion and non-contact explosion are analyzed.Finally,a damage identification method of the dam subjected to underwater explosion based on multi-source information such as video measurement,structural modal analysis and machine learning is proposed.The main innovations are as follows:(1)A fast acquisition method of structural operational deflection shapes based on high-speed photography is proposedThe process of structural modal parameter identification based on the phase information of videos is summarized.Considering the defects of artificial supervision and interference in extracting structural operational deflection shapes by video magnification technology,the edge detection algorithm of video measurement is improved by virtual sensor method.The histogram threshold filtering method and edge detection-region labelling method are proposed,which can be used in simple and complex experimental environments respectively by high-speed photography.(2)The technology of obtaining dam modal parameters based on video measurement is proposed.The phase-based motion estimation is used to extract the micro-vibration information from the motion video of the dam and identify its natural frequencies.The digital image processing technology is used to extract the operational deflection shapes of the dam from the motion magnified video.Then the video measurement and extraction method of the dynamic parameters of the concrete dam is proposed.At the same time,the dynamic response process of the concrete dam under different environmental excitations is discussed,and the coagulation is revealed.Based on the characteristics of in-plane and out-of-plane motion of the dam,a method to ensure that only in-plane motion of dam is photographed by camera calibration technology is proposed.(3)The typical failure modes of the concrete dam to underwater explosion is generalized.Considering the strain rate effect of concrete under high loading rate of explosion,the dynamic analysis model of explosive-water-air-foundation-dam to underwater explosion based on Lagrangian-Eulerian coupling algorithm is established.Combining with the complex process of explosive initiation,shock wave propagation,shock wave-structure interaction,the damage effect evaluation models of the concrete dam under different reservoir water level are established and analyzed.The influence of resevior water level on the protective performance of concrete dams is studied.The damage mechanism and spatial distribution characteristics of concrete dams to underwater contact/non-contact explosion are revealed.The typical failure modes of concrete gravity dams and concrete arch-gravity dams to underwater explosion are proposed.(4)A fast identification technique for underwater explosion damage of concrete dams is proposed.Considering the frequency and mode shape characteristics of concrete dams under different damage states,a damage identification model based on machine learning algorithm is established,and a fast identification method of damage location and ranage based on video measurement technology is proposed.The multi-damage pattern recognition technology of dam explosion based on particle swarm optimization parameter selection is preliminarily explored.