Current Issue : January - March Volume : 2020 Issue Number : 1 Articles : 5 Articles
Underwater structural damage inspection has mainly relied on diver-based visual\ninspection, and emerging technologies include the use of remotely operated vehicles (ROVs) for\nimproved efficiency. With the goal of performing an autonomous and robotic underwater\ninspection, a novel Tactile Imaging System for Underwater Inspection (TISUE) is designed,\nprototyped, and tested in this paper. The system has two major components, including the imaging\nsubsystem and the manipulation subsystem. The novelty lies in the imaging subsystem, which\nconsists of an elastomer-enabled contact-based optical sensor with specifically designed artificial\nlighting. The completed TISUE system, including optical imaging, data storage, display analytics,\nand a mechanical support subsystem, is further tested in a laboratory experiment. The experiment\ndemonstrates that high-resolution and high-quality images of structural surface damage can be\nobtained using tactile â??touch-and-senseâ?? imaging, even in a turbid water environment. A deep\nlearning-based damage detection framework is developed and trained. The detection results\ndemonstrate the similar detectability of five damage types in the obtained tactile images to images\nobtained from regular (land-based) structural inspection....
Shear deformable beams have been widely used in engineering applications. Based on\nthe matrix structural analysis (MSA), this paper presents a method for the buckling and\nsecond-order solutions of shear deformable beams, which allows the use of one element per\nmember for the exact solution. To develop the second-order MSA method, this paper develops the\nelement stability stiffness matrix of axial-loaded Timoshenko beamâ??columns, which relates the\nelement-end deformations (translation and rotation angle) and corresponding forces (shear force\nand bending moment). First, an equilibrium analysis of an axial-loaded Timoshenko beamâ??column\nis conducted, and the element flexural deformations and forces are solved exactly from the\ngoverning differential equation. The element stability stiffness matrix is derived with a focus on the\nelement-end deformations and the corresponding forces. Then, a matrix structural analysis\napproach for the elastic buckling analysis of Timoshenko beamâ??columns is established and\ndemonstrated using classical application examples. Discussions on the errors of a previous\nsimplified expression of the stability stiffness matrix is presented by comparing with the derived\nexact expression. In addition, the asymptotic behavior of the stability stiffness matrix to the\nfirst-order stiffness matrix is noted....
The alkaliâ??silica reaction is a chemical phenomenon that, by inducing expansion and the\nformation of cracks in concrete, can have a severe impact on the safety and functioning of existing\nconcrete dams. Starting from a phenomenological two-phase isotropic damage model describing the\ndegradation of concrete, the effects of alkali-silica reaction in an existing concrete gravity dam are\nevaluated and compared with real monitoring data. Considering the real temperature and humidity\nvariations, the influence of both temperature and humidity are considered through two uncoupled\ndiffusion analyses: a heat diffusion analysis and a moisture diffusion analysis. The numerical analyses\nperformed with the two-phase damage model allow for prediction of the structural behaviour, both\nin terms of reaction extent and increase of crest displacements. The crest displacements are compared\nwith the real monitoring data, where reasonably good agreement is obtained....
Based on theories of explosive mechanics and rock fracture mechanics, the influence mechanism of rock strength on the\npropagation length of the primary crack in the directional fracture blasting with slotted cartridge has been investigated deeply to\npropose the relation equation between the rock strength and the propagation length of the primary crack. Theoretically, the\nmaximum length a^m of the primary crack increases with the enhancing rock strength parameters. The explicit dynamic analysis\nsoftware LS-DYNA has been used to simulate the slotted cartridge blasting in the mudstone, sandstone, and granite with different\nstrengths in order to reveal the effect of rock strength on the propagation length and velocity of the primary crack and the stress\ndistribution characteristics in rock. The numerical results show the primary crack easily bifurcates and attain a much shorter\npropagation length in the mudstone with the minimum strength, and there are radial cracks appearing in the nonslotted direction.\nWhen rock strength rises, the propagation length, velocity, and duration of the primary crack and the concentration degree of\neffective stress in the slotted direction will all increase in the sandstone and granite, but there is an opposite influence trend of rock\nstrength in the stage of the initial guide crackâ??s formation. The cracking velocity has an overall oscillation downtrend whose swing\namplitude enhances clearly with the increasing rock strength, signifying the more unsteady propagation of the primary crack in\nthe higher strength rock....
At constant shear rate, the process of deformation of the paste slurry is divided into two stages: one is the initial structural failure\nprocess with increasing shear stress; the other is the thixotropic process with decreasing shear stress after yielding. Based on\nexperiments, the mechanical response characteristics of the paste slurry in the initial structural failure process under different\nshear rate conditions were studied in this paper. At the same time, according to the Maxwell model, the stress-time model\nequation describing the initial structure failure stage of the paste was deduced and the constant shearing test was carried out on the\npaste slurry at different mass concentrations; the model equation was used to fit the test data of the initial stress increment stage.\nThe results showed that the model equation had higher prediction accuracy and better popularity. In the initial structural failure\nstage, the paste had a nonlinear stress-time relationship. At different shear rates (0.05, 0.5, and 1 s^- 1), the lower the rotation speed,\nthe smoother the curve, and the slurry at various stages in the yielding process could be more clearly reflected; in the range of low\nconstant shear rate (0.03, 0.05, and 0.07 s^- 1), the initial stress and yield stress of the paste increased with the increase of shear rate at\nthe same mass concentration, and the time to yield was shorter. The yield stress increased exponentially with mass concentration....
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