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RISS 인기검색어
- 검색키워드
- 저자 : Zhizhen Liu (검색결과 4 건)
- 무료
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- 유료
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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.
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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
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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.
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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.
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