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RISS 인기검색어
- 검색키워드
- 저자 : Yukun Ji (검색결과 3 건)
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Yukun Ji,Guoqing Zhou,Matthew R. Hall,Veerle Vandeginste,Xiaodong Zhao 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.4
Frost heave induced ground surface uplift can have a destructive impact on infrastructures when freezing methods are used for underground construction. The complexity of overburden pressure and the coupled heat and mass transport interaction and their relation to different water flow rates make frost heave modelling an interesting but challenging task. A frost heave model describing phase transition and multiphase interactions (liquid-crystal-soil matrix) is presented in this paper and used to investigate the kinetic growth of the ice lens. By introducing water activity determined growth rate of ice crystals, the micro- and meso-physical mechanisms underlying ice lens growth involve ice crystal nucleation, crystallization, phase transition, and water migration in the frozen fringe are explored. This work indicates that the frozen fringe thickness, the ice crystals growth and the cryogenic-suction in the frozen fringe are particularly significant in determining the ice lens growth kinetics (frost heave) under different overburden pressures. The variation in ice lens growth under various overburden pressures appears to be controlled by the water flow path, cryogenic-suction, and permeability of the frozen fringe. This research reveals the kinetic growth of the ice lens, and helps to evaluate and mitigate geological hazards when artificial ground freezing is applied.
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Yukun Tao,Feifei Yang,Ping He,Congshan Li,Yuqi Ji 제어·로봇·시스템학회 2020 International Journal of Control, Automation, and Vol.18 No.9
This paper presents a distributed adaptive neural tracking consensus control strategy for a class of stochastic nonlinear multiagent systems with whole state time delays, input and output constrains. The considered systems are involved in the existence of whole state delays and stochastic disturbances, which makes the controller design more difficult and complex. Firstly, time delays are related to unknown dynamic interactions with the whole states of the agent systems, and novel Lyapunov-Krasovskii functionals are constructed. Secondly, the smooth asymmetric saturation nonlinearity is given based on Gaussian error function, output constraints are achieved via barrier Lyapunov functions, and neural networks are utilized to deal with the completely unknown nonlinearities and stochastic disturbances. Then, based on Lyapunov stability theory, a delay-independent adaptive controller is developed via Lyapunov-Krasovskii functionals and backstepping technique, and it reduces the complexity of learning parameters. It is proved that the proposed approximation-based controller can guarantee that all closed-loop signals are cooperatively semi-globally uniformly ultimately bounded (CSGUUB), and the tracking errors between the followers and the leaders eventually converge to a small neighbourhood around the origin. Finally, simulation studies are carried out, and the simulation results verify the correctness and effectiveness of the proposed Strategy.
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Field Test on Uplift Bearing Capacity of Rock-Socketed Belled Piles
Qinke Wang,Jianlin Ma,Zili Xiao,Wenlong Chen,Yukun Ji 대한토목학회 2020 KSCE JOURNAL OF CIVIL ENGINEERING Vol.24 No.8
The thick sandstone with an upper layer of clay (2 m to 3 m) was identified at the transmission line projects in western China. Tower foundations are affected by extreme weather such as strong wind and snow all the year round, so the research of foundation uplift is very significant. Belled piles are widely used in the area due to its high uplift bearing capacity, however, further research studies regarding the uplift bearing capacity of the belled piles in this special scenario still need to be conducted. The uplift bearing characteristics of five rock-socketed belled piles were studied by field testing method. The load-displacement curves, fitting analysis of load-displacement curves, change rate of pullout stiffness, distribution of axial force alone the pile, and pile side friction were analyzed. Observation results show that the load-displacement curves of rock-socketed belled piles are steeply changed. Moreover, we find that the hyperbolic model can provide a good fitting result for load-displacement curves, and the ultimate uplift bearing capacity is suggested to be predicted by using a reduction parameter of 0.64 − 0.85. Both uplift bearing capacity coefficient Nu and utilization ratio of pile material ηincrease with the increase of L/d under a same diameter, while the growth rate decreases. In this paper, the significant size effect is observed with increasing of pile diameter. The change rate of pullout stiffness-displacement curves are consistent with the trend of the safety factor-displacement curves, and can be fitted by power function model. Additionally, the change rate of pullout stiffness at the limit state will decrease to around 154 in this study, which can be used as the instability threshold for the rock-socketed belled piles in a similar soil foundation.
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