Assessing Resilience of Inter-Domain Routing System under Regional Failures

( Yujing Liu ),( Wei Peng ),( Jinshu Su ),( Zhilin Wang ) 한국인터넷정보학회 2016 KSII Transactions on Internet and Information Syst Vol.10 No.4

Inter-domain routing is the most critical function of the Internet. The routing system is a logical network relying on the physical infrastructure with geographical characteristics. Nature disasters or disruptive accidents such as earthquakes, cable cuts and power outages could cause regional failures which fail down geographically co-located network nodes and links, therefore, affect the resilience of inter-domain routing system. This paper presents a model for regional failures in inter-domain routing system called REFER for the first time. Based on REFER, the resilience of the inter-domain routing system could be evaluated on a finer level of the Internet, considering different routing policies of intra-domain and inter-domain routing systems. Under this model, we perform simulations on an empirical topology of the Internet with geographical characteristics to simulate a regional failure locating at a city with important IXP (Internet eXchange Point). Results indicate that the Internet is robust under a city-level regional failure. The reachability is almost the same after the failure, and the reroutings occur at the edge of the Internet, hardly affecting the core of inter-domain routing system.

Computations of Losses and Temperatures in the Core Ends of a High Voltage Turbo-generator

Liu Yujing,Hjarne Stig The Korean Institute of Electrical Engineers 2005 KIEE International Transactions on Electrical Mach Vol.b5 No.4

The work described in this paper is to investigate the additional iron losses and consequent temperatures in core ends of a turbo-generator wound with high voltage cables. Electromagnetic calculations are made with 3D FE models, which include the lamination material with anisotropic properties both in magnetic permeability and electric conductivity. The models also include the geometry of the stator teeth and eventually the axial steps designated to reduce the core end losses. The 3D model of the rotor consists of field windings with straight in-slot parts and end windings. The thermal models are simplified into two dimensions and include the heat sources dumped from the 3D electromagnetic solutions. The influences of power factor on additional iron losses are studied for this cable wound machine and conventional machines. The calculation results show that the additional iron losses can be reduced to about $15\%$ by introducing some small steps around the airgap corner of core ends.

Computations of Losses and Temperatures in the Core Ends of a High Voltage Turbo-generator

Yujing Liu,Stig Hjarne 대한전기학회 2005 KIEE International Transactions on Electrical Mach Vol.5-B No.4

Collaborative fabrication of poly(L-proline)s with well-defined mesopores and hydrophobicity: Synergistic effect of mesoporous confinement and hydrophobic micro-environment on organic transformations

Zhongqiu Liu,Yuanyuan Yu,Shengnan Li,Yaqi Liu,Guoqiang Zhang,Long Han,Yujing Liu,Jinmao You,Anguo Ying 한국공업화학회 2021 Journal of Industrial and Engineering Chemistry Vol.104 No.-

The preparation of materials with a well-defined mesoporous structure and hydrophobicity is of greatsignificance for heterogeneous catalyst development, yet there still remains a challenge for fabricatingthe above materials without using templates. Herein, the polymerization of L-proline-functionalizedmonomer with crosslinkers containing variable alkyl-bridged length (n = 2,4,6,8) and vinyl-modifiedFe3O4 nanoparticles to construct mesoporous poly(L-proline)s (MPLPs) has been reported for the firsttime. The resultant MPLPs were analyzed by characterization methods, suggesting that MPLPs with awell-defined mesoporous structure and unique hydrophobicity were successfully constructed by synergisticregulation of vinyl-modified Fe3O4 nanoparticles and crosslinkers with alkyl-bridged length of 6carbon atoms, in which vinyl-modified Fe3O4 nanoparticles as structural reinforcer plays a vital rolefor the mesoporous formation. Moreover, the resultant MPLPs were found to be efficient catalysts forone-pot synthesis of functionalized spiroindolones and olefins. The kinetic study and the water contactangle indicate the mesoporous confinement and hydrophobic micro-environment in organic transformations. Hence, the high activity of MPLPs is ascribed to synergistic effect of mesoporous confinement andhydrophobic micro-environment, and the adsorption experiment results further confirm this synergisticcatalysis. This work promotes a textural engineering approach to the development of multifunctionalmaterials with well-defined mesopores and hydrophobicity.

Low-Carbon Economic Dispatch of an Integrated Energy System Based on Carbon Emission Flow Theory

Liu Zheyuan,Xing Haijun,Luo Yangfan,Ye Yujing,Shi Yusong 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.3

To address the problem of low carbon economic dispatch of integrated energy systems, carbon emission flow theory is introduced into the optimal dispatch of integrated energy systems. Firstly, the carbon emission flow model is used to calculate the carbon emissions of each load in the framework of the electricity-gas integrated energy system. Secondly, the Shapley value method is introduced into the integrated energy system carbon trading model to analyze its incentive effect on emission reduction. Finally, a bi-level dispatching model of the integrated energy system is established, with the upper level being the grid and gas network dispatching model with the minimum operating cost as the objective function, and the lower level being the energy hub dispatching model with the minimum operating cost as the objective function. Low carbon economic dispatching is carried out with the objective function of minimizing operating costs. The model is verified through arithmetic examples to have the effect of improving energy utilization, reducing operating costs, and reducing carbon emissions, and can achieve low carbon economic operation.

State Feedback Design for Nonlinear Quadratic Systems with Randomly Occurring Actuator Saturation

Yujing Shi,Yueru Li,Shanqiang Li,Hongyu Liu 제어·로봇·시스템학회 2017 International Journal of Control, Automation, and Vol.15 No.3

This paper is concerned with the problem of state feedback control for nonlinear quadratic systemswith randomly occurring actuator saturation. The considered actuator saturation is assumed to occur in a randomway, and the randomly occurring rates of the saturation are time-varying with known upper and lower bounds. Byusing the Lyapunov approach, a sufficient condition is given to guarantee that the closed-loop system is locallyasymptotically stable in mean-square sense. The desired controller gain can be obtained in terms of the solutionsto certain linear matrix inequalities. Finally, a simulation example is provided to show the effectiveness of theproposed control scheme.

Effects of intersection and dead-end of fractures on nonlinear flow and particle transport in rock fracture networks

Richeng Liu,Yujing Jiang,Bo Li 한국지질과학협의회 2016 Geosciences Journal Vol.20 No.3

Fluid flow tests were conducted on three artificial rock fracture network models to visually investigate the behaviors of fluid flow and solute transport within the fracture intersections, by using the visualization techniques with a CCD camera. Numerical simulations by solving the Navier-Stokes equations were performed to simulate the fluid flow and solute transport based on the experimental models, and to extensively estimate the effects of fracture intersection and dead-end in fracture networks. The results show that for the crossed fracture models, when the Reynolds number (Re) of the inlet is larger than 1, a nonlinear flow regime starts to appear where the proportion of the flow rates in the two outlets change nonlinearly. When calculating the fluid flow in discrete fracture network (DFN) models, it is found that the critical condition of applying the local cubic law to model fluid flow in each single fracture in DFNs is J ≤ 10–5, where J is the hydraulic gradient. Beyond this value, the deviation of applying the cubic law increases remarkably with increasing hydraulic gradient. The effects of dead-ends of fractures on fluid flow are negligible, however, they have a strong impact on the breakthrough curves of particles in DFNs with the relative time deviation rate in the range of 5–35%.

Autogenous Shrinkage and Crack Resistance of Carbon Nanotubes Reinforced Cement‑Based Materials

Yanming Liu,Tao Shi,Yujing Zhao,Yuan Gu,Zhifang Zhao,Jiabin Chen,Bingmiao Zheng,Shichong Shi 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.5

Cracking caused by shrinkage deformation of cement-based materials at early age is a major problem leading to material failure in restrained conditions. Carbon nanotubes (CNTs) are incorporated into cement-based materials, and the autogenous shrinkage and crack resistance of the new composite materials obtained by linear shrinkage and ring tests are studied to solve the destruction of the materials caused by the shrinkage of cement-based materials. The results showed that addition of CNTs significantly inhibited the autogenous shrinkage of cement-based materials with maximum reduction rate above 40%. CNTs also significantly improved the cracking resistance of cement-based materials. The optimal effect was noticed at CNTs content of 0.1 wt%. The incorporation of CNTs not only inhibits the autogenous shrinkage of cement-based materials, but also inhibits the drying shrinkage of cement-based materials to some extent. Therefore, carbon nanotubes have the potential to solve the destruction of materials caused by shrinkage of cement-based materials.

Visualized experimental investigation on the hydraulic characteristics of two-phase flow in a single smooth and single rough rock fractures

Chen Wang,Yujing Jiang,Jiankang Liu,Changsheng Wang,Satoshi Sugimoto 한국지질과학협의회 2021 Geosciences Journal Vol.25 No.3

In present engineering applications, calculations of hydraulic properties in two-phase flow are still highly dependent on empirical or semi-empirical equations obtained from experiments. However, the empirical equations that can reproduce the experiment data on a certain fracture specimen may have errors on other specimens. Researchers have obtained results that show quite different evolution forms of hydraulic characteristics of two-phase flow, which is induced by the variety of the influencing factors in two-phase flow. This paper aims at expanding the experimental results on the hydraulic characteristics of two-phase flow in rock fractures. With a newly developed experiment system, visualized two-phase flow experiments were introduced. The difference in the surface morphology of the fractures leads to totally different flow structures, which indicates the role of capillary pressure differs due to different fracture surfaces. The relative permeability in the rough specimen approximately follows the Corey model, which confirmed that the pressure drop is in this rough fracture is dominated by the capillary pressure, but the relative permeability is not only the function of saturation, but also the function of water flow velocities. However, the relative permeability is not perfect for evaluating the difference of two-phase hydraulic characteristics induced by the fracture surface morphology. On the contrary, the Lockhart-Martinelli model is appropriate for evaluating the difference in the two-phase hydraulic characteristics between the smooth fracture and the rough fracture, which indicates that the two-phase flow turbulence is obviously increased by the fracture roughness.

Mechanism of shear deformation, failure and energy dissipation of artificial rock joint in terms of physical and numerical consideration

Xuepeng Zhang,Yujing Jiang,Gang Wang,Jiankang Liu,Dong Wang,Changsheng Wang,Satoshi Sugimoto 한국지질과학협의회 2019 Geosciences Journal Vol.23 No.3

The physical and mechanical change processes of rock are closely related to energy transformation, and its deformation and failure is an instability phenomena driven by energy exchange. This study investigated mechanism of shear deformation, failure and energy dissipation of joint using both physical and numerical direct shear tests under constant normal load (CNL) condition. Three kinds of joint surface were artificially prepared. An acoustic emission system was employed to monitor acoustic emission in physical test, and rupture frequency was recorded in numerical test to represent micro-crack development. By research of numerical micro-crack development accompanied with physical acoustic emission results, mechanism of shear deformation and failure of joints were illustrated schematically. By definition of dissipation energy, captured using the particle flow code (PFC2D), energy releasing and dissipation were discussed with microscopic damage evolution of joints. Results showed that joints under shearing present a dissipation trend of four stages including a slow rise stage, a rapid rise stage, a shock rise stage and a rapid decline stage.