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Lei Xu,Lei Xu,Wen-Da Wang,Jian-Gang Sun 한국강구조학회 2017 International Journal of Steel Structures Vol.17 No.4
The present study established a numerical investigation on the behavior of concrete filled steel tube reinforced concrete (CFSTRC) columns subjected to fire. A finite element analysis (FEA) model was built to simulate the performance of CFSTRC columns under combined loading and fire. The FEA model was verified by the experimental results of CFSTRC columns subjected to fire. The comparison demonstrated an acceptable accuracy for the proposed FEA model. Afterwards, the FEA model was used to analyze the failure modes, the redistribution of internal force, the changes and development of the stress and strain, and the contact stress between the tube and concrete of CFSTRC columns subjected to fire. Influencing factors that may affect the bearing capacity of the CFSTRC columns subjected to fire were analyzed. The bearing capacity and stiffness of the CFSTRC columns gradually decreased in the fire; the parameters such as the fire duration time, sectional dimension, slenderness ratio, and sectional core area ratio significantly influenced the bearing capacity of the CFSTRC columns. Finally, a simplified calculating formula was proposed to calculate the influence factors of the bearing capacity of the CFSTRC columns subjected to ISO-834 standard fire. The formula-calculated results were well in agreement with the finite element analysis results, which provide a simple and feasible method for evaluating the fire-resistance design of these types of components in practical engineering.
CHISELED NICKEL HYDROXIDE NANOPLATES GROWTH ON GRAPHENE SHEETS FOR LITHIUM ION BATTERIES
LEI-LEI TIAN,XIAN-YONG WEI,QUAN-CHAO ZHUANG,CHAO WU,RUI-LUN XIE,ZHI-MIN ZONG,YONG-LI CUI,SHI-GANG SUN 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2013 NANO Vol.8 No.6
The morphologies and structures of Ni(OH)2–graphene hybrid materials were tailored by using different mineralizers in this work. It was revealed that the synergic effects of the highly oxidized graphene sheets and the mineralizers played a crucial role in controlling the morphology and structure of the nanocomposites, and Na2CO3 is a very effective mineralizer for growing chiseled 2D nanoplates of Ni(OH)2 on graphene sheets. When produced with NaOH, fragmental Ni(OH)2 crystals with irregular shapes erratically decorated on graphene sheets. In contrast, chiseled Ni(OH)2 hexagonal nanoplates grown on graphene sheets were obtained when Na2CO3 was used as the mineralizer. These unique 2D–2D nanoarchitectures with higher contact area between the nanocrystals and graphene substrate can increase the interfacial interaction and then efficiently improve the structural stability of the composite material, thus exhibiting an enhanced Li storage capacity and excellent cycling performance of 562 mAh g-1 after the 36th cycle.
Topology Optimization of the Plate under Bending Moment by Using P1-nonconforming Element
Lei Chen(첸레이),Gang-Won Jang(장강원),Tae Hyun Baek(백태현) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.5
When the Mindlin model is applied to analyze the thin plate under bending moment, the displacement of plate is much lower than the exact value. This phenomenon is caused by shear locking of model. Here, a new nonconforming quadrilateral element P1, which is one kind of discontinuous element and owns the Poisson locking-free property, was applied to Mindlin plate. The results prove that reduced P1- nonconforming element can solve shear locking problem. Topology optimal design of plate under bending moment was based on P1 nonconforming element, whose purpose was to obtain the minimum compliance for a given mass of plate. Topology optimal shape of the plate is verified by some typical bending plate model. This paper presents a new method to solve shear locking problem of Mindlin plate and it can be used to solve other domains.
Torque Ripple Suppression Method for BLDCM Drive Based on Four-Switch Three-Phase Inverter
Lei Pan,Hexu Sun,Beibei Wang,Gang Su,Xiuli Wang,Guili Peng 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.4
A novel inverter fault-tolerant control scheme is proposed to drive brushless DC motor. A fault-tolerant inverter and its three fault-tolerant schemes (i.e., phase A fault-tolerant, phase B fault-tolerant, and phase C fault-tolerant) are analyzed. Eight voltage vectors are summarized and a voltage vector selection table is used in the control scheme to improve the midpoint current of the split capacitors. A stator flux observer is proposed. The observer can improve flux estimation, which does not require any speed adaptation mechanism and is immune to speed estimation error. Global stability of the flux observer is guaranteed by the Lyapunov stability analysis. A novel stator resistance estimator is incorporated into the sensorless drive to compensate for the effects of stator resistance variation. DC offset effects are mitigated by introducing an integral component in the observer gains. Finally, a control system based on the control scheme is established. Simulation and experiment results show that the method is correct and feasible.
Lei Yang,Yujing Jiang,Bo Li,Shucai Li,Gang Wang 대한토목학회 2013 KSCE JOURNAL OF CIVIL ENGINEERING Vol.17 No.2
Seismic behavior of bedrock foundation remains as one of the most fundamental and important problems concerning the stability and safety of nuclear power plants. The dynamic FEM (Finite Element Method) is commonly utilized in analyzing the seismic responses of bedrock; while in recent decades, the DEM (Distinct Element Method) has attracted more and more attentions, which has a better capability of simulating the sliding and separation of discontinuities in dynamic simulations. In this study, the FEM and DEM were adopted to investigate the seismic behavior of the bedrock of a nuclear power plant located in Japan, and the differences between the two methods in dynamic simulations were illuminated. Simulation results using FEM and DEM models without discontinuities agree well with each other, exhibiting an amplification effect of intact bedrock on the seismic wave propagation. Numerical simulation results obtained from the models containing faults give similar responses of bedrock to the input seismic waves; however, the FEM model underestimates the weakening effect of discontinuities on the propagation of seismic waves due to that it cannot represent well the large deformational behavior of discontinuities. When large deformation happens due to large seismic loads, the DEM can be regarded as a better method in seismic response evaluations of bedrock with discontinuities.
Lei Pan,Beibei Wang,Gang Su,Baohua Cheng,Guili Peng 대한전기학회 2015 Journal of Electrical Engineering & Technology Vol.10 No.1
The main purpose of this paper is to describe a DTC (direct torque control) method for four-switch brushless dc motor (BLDCM) drive. In the method, a novel voltage space vector modulation scheme, an optimal switching table, and a flux observation method are proposed. Eight voltage vectors are summarized, which are selected to control BLDCM in SVPWM pattern, and an optimal switching table is proposed to improve the torque distortion caused by midpoint current of the split capacitors. Unlike conventional flux observers, this observer does not require speed adaptation and is not susceptible to speed estimation errors, especially, at low speed. Global asymptotic stability of the flux observer is guaranteed by the Lyapunov stability analysis. DC-offset effects are mitigated by introducing a PI component in the observer gains. This method alleviates the undesired current and torque distortion which is caused by uncontrollable phase. The correctness and feasibility of the method are proved by simulation and experimental results.
Bending ratcheting behavior of pressurized straight Z2CND18.12N stainless steel pipe
Lei Wang,Gang Chen,Jianbei Zhu,Xiuhu Sun,Yunhui Mei,Xiang Ling,Xu Chen 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.52 No.6
The ratcheting effect greatly challenges the design of piping components. With the assistance of the quasi-three point bending apparatus, ratcheting and the ratcheting boundary of pressurized straight Z2CND18.12N stainless steel pipe under bending loading and vertical displacement control were studiedexperimentally. The characteristics of progressive inelastic deformation in axial and hoop directions of the Z2CND18.12N stainless steel pipes were investigated. The experiment results show that the ratcheting strainoccurs mainly in the hoop direction while there is less ratcheting strain in the axial direction. Thecharacteristics of the bending ratcheting behavior of the pressure pipes were derived and compared under load control and displacement control, respectively. The results show that the cyclic bending loading and the internal pressure affect the ratcheting behavior of the pressurized straight pipe significantly under loadcontrol. In the meantime, the ratcheting characteristics are also highly associated with the cyclicdisplacement and the internal pressure under displacement control. All these factors affect not only the saturation of the ratcheting strain but the ratcheting strain rate. A series of multi-step bending ratcheting experiments were conducted under both control modes. It was found that the hardening effect of Z2CND18.12N stainless steel pipe under previous cyclic loadings no matter with high or low displacement amplitudes is significant, and the prior loading histories greatly retard the ratcheting strain and its rate under subsequent loadings. Finally, the ratcheting boundaries of the pressurized straight Z2CND18.12N stainless steel pipe were determined and compared based on KTA/ASME, RCC-MR and the experimental results.