Three-Dimensional Upper Bound Limit Analysis of Tunnel Stability with an Extended Collapse Mechanism

Zhizhen Liu,Ping Cao,Fei Wang,Jingjing Meng,Rihong Cao,Jingshuo Liu 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.12

A three-dimensional collapse mechanism that can consider a combined collapse of the tunnel roof and the side walls is proposed in this work. The three-dimensional upper bound support pressure is formulated with the power balance principal in the upper bound theorem. The nonlinear Mohr-Coulomb failure criterion is used to replace the commonly used linear Mohr-Coulomb failure criterion. The method has been validated by a series of examples, in which the three-dimensional collapse mechanism and support pressures are in a good agreementwith the numerical results and solutions found in the literatures. Furthermore, sensitivity analyses of the geotechnical and geometrical parameters on the support pressure areconducted and the collapsing range is measured. The results show that a higher value of nonlinear failure coefficient, tensile strength, initial cohesion and tangential internal friction angle can increase tunnel stability, while tunnel stability is threatened by a higher value of burial depth, unit weight, tunnel width and height. The predicted collapse range increases noticeably with the increase of the nonlinear coefficient. This study is of great significance for predicting the three-dimensional safety support pressure and collapse mechanism of tunnel.

Comparative Study of Wire Arc Additive Manufactured and Wrought Ultrahigh-Strength Steels: Flow Behavior and Microstructure Evolution

YiBo Xiong,DongXu Wen,ZhiZhen Zheng,ChaoYuan Sun,Jing Xie,JianJun Li 대한금속·재료학회 2023 METALS AND MATERIALS International Vol.29 No.10

The combination of wire arc additive manufacturing (WAAM) technology with traditional manufacturing process providesa promising method for fabricating the large and complex parts with the advantages of high performance, time-saving, lowcost and high material utilization. In order to acquire the optimal hybrid manufacturing process, the comparative study offlow behaviors and microstructure evolution of wrought and WAAMed ultrahigh-strength (UHS) steels is carried out underthe temperatures of 920–1160 ℃ and strain rates of 0.01–10 s−1 . The results show that the coarse prior austenite columnargrains and carbides in the initial microstructure of the WAAMed UHS steel contribute to the higher flow stress and slowerdynamic recrystallization (DRX) kinetics during hot deformation as compared to the wrought UHS steel. The hot activationenergy under the peak stress of the wrought and WAAMed UHS steels is estimated to be 332.3 kJ/mol and 374.1 kJ/mol,respectively. On the basis of the hot processing maps, the common optimal processing window for WAAMed and wroughtUHS steels is determined as the temperatures of 1060–1160 oC and strain rates of 0.08–0.66 s−1 . Under these deformationparameters, the microstructures of WAAMed and wrought UHS steels consist of fine DRXed grains, and the DRX behaviorsare both dominated by the discontinuous DRX and continuous DRX mechanisms.

A Magnetic Energy Recovery Switch Based Terminal Voltage Regulator for the Three-Phase Self-Excited Induction Generators in Renewable Energy Systems

Yewen Wei,Longyun Kang,Zhizhen Huang,Zhen Li,Miao miao Cheng 전력전자학회 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

Distributed generation systems (DGSs) have been getting more and more attention in terms of renewable energy use and new generation technologies in the past decades. The self-excited induction generator (SEIG) occupies an important role in the area of energy conversion due to its low cost, robustness and simple control. Unlike synchronous generators, the SEIG has to absorb capacitive reactive power from the outer device aiming to stabilize the terminal voltage at load changes. This paper presents a novel static VAR compensator (SVC) called a magnetic energy recovery switch (MERS) to serve as a voltage controller in SEIG powered DGSs. In addition, many small scale SEIGs, instead of a single large one, are applied and devoted to promote the generation efficiency. To begin with, an expandable mathematic model based on a d-q equivalent circuit is created for parallel SEIGs. The control method of the MERS is further improved with the objective of broadening its operating range and restraining current harmonics by parameter optimization. A hybrid control strategy is developed by taking both of the stand-alone and grid-connected modes into consideration. Then simulation and experiments are carried out in the case of single and double SEIG(s) generation. Finally, the measurement results verify that the proposed DGS with SVC-MERS achieves a better stability and higher feasibility. The major advantages of the mentioned variable reactive power supplier, when compared to the STATCOM, include the adoption of a small DC capacitor, line frequency switching, simple control and less loss.

Research on Subcutaneous Pulse Shape Measurement by Near-infrared Moiré Technique

Ying-Yun Chen,Zhizhen Liu,Jian Du,Rong-Seng Chang 한국광학회 2015 Current Optics and Photonics Vol.19 No.2

A pulse is generated when the heart pumps blood into the arterial system. The heart pumps blood onlywhen it contracts, not when it relaxes; therefore, blood enters the arterial system in a cyclical form. Arterybeating is visible in some parts of the body surface, such as the radial artery of the wrist. This papermainly uses the feature in which near-infrared spectroscopy penetrates skin to construct a non-invasivemeasurement system that can measure small vibration in the subcutaneous tissue of the human body, andthen uses it for the pulse measurement. This measurement system uses the optical moiré principle, togetherwith the fringe displacement made by small vibration in the subcutaneous tissue, and an image analysisprogram to calculate the height variation from small vibrations in the subcutaneous tissue. It completesa measurement system that records height variation with time, and that together with a fast Fouriertransform (FFT) program, they can convert the pulse waveform generated by vibration (time-amplitude)to heartbeat frequency (frequency-amplitude). This is a new and non-invasive medical assistance systemfor measuring the pulse of the human body, with the advantages of being simple, fast, safe and objective

A Magnetic Energy Recovery Switch Based Terminal Voltage Regulator for the Three-Phase Self-Excited Induction Generators in Renewable Energy Systems

Wei, Yewen,Kang, Longyun,Huang, Zhizhen,Li, Zhen,Cheng, Miao miao The Korean Institute of Power Electronics 2015 JOURNAL OF POWER ELECTRONICS Vol.15 No.5

Distributed generation systems (DGSs) have been getting more and more attention in terms of renewable energy use and new generation technologies in the past decades. The self-excited induction generator (SEIG) occupies an important role in the area of energy conversion due to its low cost, robustness and simple control. Unlike synchronous generators, the SEIG has to absorb capacitive reactive power from the outer device aiming to stabilize the terminal voltage at load changes. This paper presents a novel static VAR compensator (SVC) called a magnetic energy recovery switch (MERS) to serve as a voltage controller in SEIG powered DGSs. In addition, many small scale SEIGs, instead of a single large one, are applied and devoted to promote the generation efficiency. To begin with, an expandable mathematic model based on a d-q equivalent circuit is created for parallel SEIGs. The control method of the MERS is further improved with the objective of broadening its operating range and restraining current harmonics by parameter optimization. A hybrid control strategy is developed by taking both of the stand-alone and grid-connected modes into consideration. Then simulation and experiments are carried out in the case of single and double SEIG(s) generation. Finally, the measurement results verify that the proposed DGS with SVC-MERS achieves a better stability and higher feasibility. The major advantages of the mentioned variable reactive power supplier, when compared to the STATCOM, include the adoption of a small DC capacitor, line frequency switching, simple control and less loss.

Parallel-Connected Magnetic Energy Recovery Switch Used as a Continuous Reactive Power Controller

Yewen Wei,Bo Fang,Longyun Kang,Zhizhen Huang,Teguo liu 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

Power quality promotion has received increasing attention because of the wide use of semiconductor devices in recent decades. Reactive power regulation is crucial to ensuring the stable operation of power systems. In this study, a continuous reactive power controller, which is referred to as a parallel-connected magnetic energy recovery switch (MERS), is developed to regulate voltage or power factor in power grids. First, the operating principle is introduced, and a mathematical model is built. Second, a new control method for restraining current harmonics and the peak voltages of capacitors is presented. Using the proposed method, the MERS shows a wide range in terms of reactive power compensation. Finally, the performance of the proposed controller is demonstrated through computer simulations and experiments. Unlike STATCOMs, the proposed controller entails low losses, adopts a small dc capacitor, and offers ease of use.

Parallel-Connected Magnetic Energy Recovery Switch Used as a Continuous Reactive Power Controller

Wei, Yewen,Fang, Bo,Kang, Longyun,Huang, Zhizhen,liu, Teguo The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.4

Power quality promotion has received increasing attention because of the wide use of semiconductor devices in recent decades. Reactive power regulation is crucial to ensuring the stable operation of power systems. In this study, a continuous reactive power controller, which is referred to as a parallel-connected magnetic energy recovery switch (MERS), is developed to regulate voltage or power factor in power grids. First, the operating principle is introduced, and a mathematical model is built. Second, a new control method for restraining current harmonics and the peak voltages of capacitors is presented. Using the proposed method, the MERS shows a wide range in terms of reactive power compensation. Finally, the performance of the proposed controller is demonstrated through computer simulations and experiments. Unlike STATCOMs, the proposed controller entails low losses, adopts a small dc capacitor, and offers ease of use.

Designing and implementing scaffolding tools for pre-service teachers in technology-enhanced student-centered learning environments

Suhkyung Shin,Sungwon Shin,Thomas A. Brush,Zhizhen Zhang 한국교육공학회 2012 한국교육공학회 학술대회발표자료집 Vol.2012 No.1

High-Temperature Deformation Characteristics and Constitutive Model of an Ultrahigh Strength Steel

YiBo Xiong,DongXu Wen,JianJun Li,Kang Wang,ZhiZhen Zheng 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.10

The high-temperature deformation characteristics of an ultrahigh strength steel is studied by hot compression tests under thedeformation temperatures of 920–1160 °C and strain rates of 0.01–10 s−1. By employing the metalloscope and transmissionelectron microscope, the influences of deformation parameters (deformation temperature and strain rate) upon microstructureevolution are analyzed in detail. Results show that the hot deformation activation energy of the studied steel is estimated as332.3 kJ/mol. The microstructure presents the typical dynamic recrystallization (DRX) features, and the DRX behaviorsare mainly dominated by the discontinuous DRX mechanism under different deformation parameters. Under the low strainrate or the high deformation temperature, the continuous DRX behavior caused by the rotation of subgrains takes place. Forforecasting the deformation stress of the studied steel, a physically-based constitutive model is constructed by combiningdislocation density theory and DRX kinetics. The reproduced deformation stresses well close to the measured data indicatesthat the developed physically-based constitutive model enjoys a preferred prediction ability to forecast the high-temperaturedeformation behaviors for the studied steel.