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RISS 인기검색어
- 검색키워드
- 저자 : Zhenyu Niu (검색결과 5 건)
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Mesh generation of porous metals from X-ray computed tomography volume data
Zhenyu Niu,Hiromasa Suzuki,Yutaka Ohtake,Takashi Michikawa 대한기계학회 2014 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.28 No.7
Recently, to meet the requirement of machine industry, there has been an increased focus on the development of porous metal as ahigh-strength material despite its low density. To evaluate its properties and quality, material testing is usually conducted. However, it ismore efficient to perform computer simulation evaluations using finite element analysis. The X-ray computed-tomography scanningtechnique enables us to obtain the information regarding the internal structure of the metal. Furthermore, a reconstruction algorithm producesvolume data of the test object. In general, conventional methods are utilized to generate mesh data from volume data for finiteelement analysis, but a key drawback is that they generate too many elements, resulting in high computational cost. We propose an approachto generate meshes for porous structures by modeling each pore using spheres from volume data.
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Mesh Generation of Porous Metals from X-ray Computed Tomography Volume Data
Zhenyu Niu,Hiromasa Suzuki,Yutaka Ohtake,Takashi Michikawa (사)한국CDE학회 2013 한국CAD/CAM학회 국제학술발표 논문집 Vol.2010 No.8
Recently, to meet the requirement of machine industry, there has been an increased focus on the development of porous metal as a high-strength material despite its low density. To evaluate its properties and quality, material testing is usually conducted. However, it is more efficient to perform computer simulation evaluations using finite element analysis. In fact, converting a large piece of porous metal into digitized mesh data is significantly difficult because of its complex inner structure. The X-ray computed tomography scanning technique enables us to obtain the information regarding the internal structure of the metal. Furthermore, a reconstruction algorithm produces volume data of the test object. In general, conventional methods are utilized to generate mesh data from volume data, but a key drawback is that they generate too many elements, resulting in high computational cost. We propose an approach to generate meshes for porous structures by modeling each pore using spheres from volume data. Data conversion is conducted through a series of processes namely labeling, spherical approximation, shape approximation, region segmentation, and meshing. The result verifies the feasibility of the proposed method, which generates shape-approximated and finite-element-simulation-available mesh data using fewer elements.
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Wei Wang,Guangming Zhang,Yuguang Niu,Zhenyu Chen,Peiran Xie,Zhe Chen 제어·로봇·시스템학회 2022 International Journal of Control, Automation, and Vol.20 No.5
The operating flexibility of the power units is getting increasing attention from power systems especially those with large-scale fluctuating renewable energies. However, the combined heat and power (CHP) units are getting a bottleneck because their electricity productions are restricted by heat productions. This study aims to develop an electric-heat coordinated control strategy to make the CHP units more flexible. First of all, the dynamic model for a 300 MW CHP unit is set up, and its linear state-space description is obtained. A control strategy based on linear quadratic regulator (LQR) is then developed to satisfy different heat-power demands in various operating conditions. The control weights Q and R are optimized by particle swarm optimization. Moreover, the improved coordinated control strategy based on precise energy balance is put forward to increase the CHP power ramp rate considering electricity priority strategy and recovery control of the heat source. Finally, the simulation results show that the improved strategy is suitable for various CHP operating scenarios, and the case for electricity priority and heat recovery control significantly improves the unit power rate on the premise of stable heat supply. This work provides a reliable and flexible control mode for CHP units, which can support the power system stability and renewable energy integration.
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Zhu, Zhili,Cai, Xiaolin,Yi, Seho,Chen, Jinglei,Dai, Yawei,Niu, Chunyao,Guo, Zhengxiao,Xie, Maohai,Liu, Feng,Cho, Jun-Hyung,Jia, Yu,Zhang, Zhenyu American Physical Society 2017 Physical Review Letters Vol.119 No.10
<P>Contemporary science is witnessing a rapid expansion of the two-dimensional (2D) materials family, each member possessing intriguing emergent properties of fundamental and practical importance. Using the particle-swarm optimization method in combination with first-principles density functional theory calculations, here we predict a new category of 2D monolayers named tellurene, composed of the metalloid element Te, with stable 1T-MoS2-like (alpha-Te), and metastable tetragonal (beta-Te) and 2H-MoS2-like (gamma-Te) structures. The underlying formation mechanism is inherently rooted in the multivalent nature of Te, with the central-layer Te behaving more metal-like (e.g., Mo), and the two outer layers more semiconductorlike (e.g., S). We also show that the alpha-Te phase can be spontaneously obtained from the magic thicknesses divisible by three layers truncated along the [ 001] direction of the trigonal structure of bulk Te, and both the alpha- and alpha-Te phases possess electron and hole mobilities much higher than MoS2. Furthermore, we present preliminary but convincing experimental evidence for the layering behavior of Te on HOPG substrates, and predict the importance of multivalency in the layering behavior of Se. These findings effectively extend the realm of 2D materials to group-VI elements.</P>
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Li, Chenhui,Yi, Seho,Xia, Congxin,Cui, Ping,Niu, Chunyao,Cho, Jun-Hyung,Jia, Yu,Zhang, Zhenyu American Chemical Society 2016 NANO LETTERS Vol.16 No.10
<P>Quantum growth refers to the phenomena in which the quantum mechanically confined motion of electrons in metallic wires, islands, and determines their overall structural stability as well as their physical and chemical properties. Yet to date, there has been a lack of a unified understanding of quantum growth with respect to the dimensionality of the nanostructures as well as the valency of the constituent atoms. Based on a first-principles approach, we investigate the-stability of nanowires, nanoislands, and ultrathin films of prototypical metal elements. We reveal that the Friedel oscillations generated at the edges (or surfaces) of the nanostructures cause corresponding oscillatory behaviors in their stability, leading to the existence of highly preferred lengths (or thicknesses). Such magic lengths of the nanowires are further found to depend on both the number of valence electrons and the radial size, with the oscillation period monotonously increasing for alkali and group IB metals, and monotonously decreasing for transition and group IIIA-VA metals. When the radial size of the nanowires increases to reach similar to 10 A, the systems equivalently become nanosize islands, and the oscillation period saturates to that of the corresponding ultrathin films. These findings offer a generic perspective of quantum growth of different classes of metallic nanostructures.</P>
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