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Additive Manufacturing of Ceramic Structures by Laser Engineered Net Shaping

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Chinese Journal of Mechanical Engineering 2015年第6期28卷 1117-1122页

作者： NIU Fangyong wu Dongjiang MA Guangyi ZHANG Bi Key Laboratory for Precision and Non-traditional Machining Technology of Ministry of Education Dalian University of Technology Department of Mechanical Engineering University of Connecticut

Ceramic is an important material with outstanding physical properties whereas impurities and porosities generated by traditional manufacturing methods limits its further industrial applications. In order to solve this problem, direct fabrication of Al2O3 ceramic structures is conducted by laser engineered net shaping system and pure ceramic powders. Grain refinement strengthening method by doping Zr O2 and dispersion strengthening method by doping Si C are proposed to suppress cracks in fabricating Al2O3 structure. Phase compositions, microstructures as well as mechanical properties of fabricated specimens are then analyzed. The results show that the proposed two methods are effective in suppressing cracks and structures of single-bead wall, arc and cylinder ring are successfully deposited. Stable phase of α-Al2O3 and t-Zr O2 are obtained in the fabricated specimens. Micro-hardness higher than 1700 HV are also achieved for both Al2O3 and Al2O3/Zr O2, which are resulted from fine directional crystals generated by the melting-solidification process. Results presented indicate that additive manufacturing is a very attractive technique for the production of high-performance ceramic structures in a single step.

关键词： lasers net shaping alumina ceramics additive manufacturing

Effect of Heat Input on Microstructure and Mechanical Properties of Joints Made by Bypass-Current MIG Welding–Brazing of Magnesium Alloy to Galvanized Steel

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Acta Metallurgica Sinica(English Letters) 2014年第6期27卷 1038-1045页

作者： Yugang Miao Bintao wu Xiangfang Xu Duanfeng Han National Key Laboratory of Science and Technology on Underwater Vehicle Harbin Engineering University

Experiments were carried out with bypass-current MIG welding–brazing of magnesium alloy to galvanized steel to investigate the effect of heat input on the microstructure and mechanical properties of lap joints. Experimental results indicated that the joint efficiency tended to increase at first and then to reduce with the increase of heat input. The joint efficiency reached its maximum of about 70% when the heat input was 155 J/mm. The metallurgical bonding between magnesium alloy and steel was a thin continuous reaction layer, and the intermetallic compound layer consisted of Mg–Zn and slight Fe–Al phases. It is concluded that bypass-current MIG welding–brazing is a stable welding process, which can be used to achieve defect-free joining of magnesium alloy to steel with good weld appearances.

关键词： Bypass-current MIG welding–brazing Dissimilar metals Joint characteristics Interface analysis

Location-dependent effect of nickel on hydrogen dissociation and diffusion on Mg(0001)surface:Insights into hydrogen storage material design

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Journal of Magnesium and Alloys 2022年第6期10卷 1617-1630页

作者： Zongying Han Yayun wu Hao Yu Shixue Zhou College of Chemical and Biological Engineering Shandong University of Science and TechnologyQingdao 266590China State Key Laboratory of Mining Disaster Prevention and Control Co-founded by Shandong Province and the Ministry of Science and Technology Shandong University of Science and TechnologyQingdao 266590China

Density functional theory(DFT)calculations have been performed to investigate the hydrogen dissociation and diffusion on Mg(0001)surface with Ni incorporating at various *** results show that Ni atom is preferentially located inside Mg matrix rather than in/over the topmost *** calculations reveal that Ni atom locating in/over the topmost Mg(0001)surface exhibits excellent catalytic effect on hydrogen dissociation with an energy barrier of less than 0.05 *** these cases,the rate-limiting step has been converted from hydrogen dissociation to surface *** contrast,Ni doping inside Mg bulk not only does little help to hydrogen dissociation but also exhibits detrimental effect on hydrogen ***,it is crucial to stabilize the Ni atom on the surface or in the topmost layer of Mg(0001)surface to maintain its catalytic *** all the case of Ni-incorporated Mg(0001)surfaces,the hydrogen atom prefers firstly immigrate along the surface and then penetrate into the *** is expected that the theoretical findings in the present study could offer fundamental guidance to future designing on efficient Mg-based hydrogen storage materials.

关键词： Hydrogen storage Hydrogen dissociation Ni incorporation Hydrogen diffusion Mg

Efficient Algorithm for Energy-Aware Virtual Network Embedding

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Tsinghua Science and Technology 2016年第4期21卷 407-414页

作者： Shuxian Jia Guiyuan Jiang Peilan He Jigang wu School of Computer Software Technology Zhejiang University Ningbo 315048 China School of Computer Science and Engineering Nanyang Technological University 639798 Singapore State Key Laboratory of Computer Architecture Institute of Computing Technology Chinese Academy of Sciences Beijing 100190 China

Network virtualization is a promising approach for resource management that allows customized Virtual Networks （VNs） to be multiplexed on a shared physical infrastructure. A key function that network virtualization can provide is Virtual Network Embedding （VNE）, which maps virtual networks requested by users to a shared substrate network maintained by an Internet service provider. Existing research has worked on this, but has primarily focused on maximizing the revenue of the Internet service provider. In this paper, we consider energy-aware virtual network embedding, which aims at minimizing the energy consumption for embedding virtual networks in a substrate network. In our optimization model, we consider energy consumption of both links and nodes. We propose an efficient heuristic to assign virtual nodes to appropriate substrate nodes based on priority, where existing activated nodes have higher priority for hosting newly arrived virtual nodes. In addition, our proposed algorithm can take advantage of activated links for embedding virtual links so as to minimize total energy consumption. The simulation results show that, for all the cases considered, our algorithm can improve upon previous work by an average of 12.6% on acceptance rate, while the consumed energy can be reduced by 12.34% on average.

关键词： virtualization technology virtual network embedding energy efficient optimization algorithm

A novel Q-based online model updating strategy and its application in statistical process control for rubber mixing

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Chinese Journal of Chemical Engineering 2015年第5期23卷 796-803页

作者： Chunying Zhang Sun Chen Fang wu Kai Song School of Chemical Engineering and Technology Tianjin University

To overcome the large time-delay in measuring the hardness of mixed rubber, rheological parameters were used to predict the hardness. A novel Q-based model updating strategy was proposed as a universal platform to track time-varying properties. Using a few selected support samples to update the model, the strategy could dramat- ically save the storage cost and overcome the adverse influence of low signal-to-noise ratio samples. Moreover, it could be applied to any statistical process monitoring system without drastic changes to them, which is practical for industrial practices. As examples, the Q-based strategy was integrated with three popular algorithms （partial least squares （PIE）, recursive PIE （RPLS）, and kernel PIE （KPIE）） to form novel regression ones, QPLS, QRPIE and QKPLS, respectively. The applications for predicting mixed rubber hardness on a large-scale tire plant in east China prove the theoretical considerations.

关键词： Online model updating Rubber mixingQ statistic Hardness Rheological parameters Statistical process control

Effective Query Grouping Strategy in Clouds

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Journal of Computer Science & Technology 2017年第6期32卷 1231-1249页

作者： Qin Liu Yuhong Guo Jie wu Guojun Wang College of Computer Science and Electronic Engineering Hunan University Changsha 410082 China State Key Laboratory of Networking and Switching Technology Beijing University of Posts and Telecommunications Beijing 100876 China School of Computer Science Carleton University Ottawa ON K155B6 Ganada Department of Computer and Information Sciences Temple University Philadelphia PA 19122 U.S.A. School of Computer Science and Educational Software Guangzhou University Guangzhou 510006 China

As the demand for the development of cloud computing grows, more and more organizations have outsourced their data and query services to the cloud for cost-saving and flexibility. Suppose an organization that has a great number of users querying the cloud-deployed multiple proxy servers to achieve cost efficiency and load balancing. Given n queries, each of which is expressed as several keywords, and k proxy servers, the problem to be solved is how to classify n queries into k groups, in order to minimize the difference between each group and the number of distinct keywords in all groups. Since this problem is NP-hard, it is solved in mathematic and heuristic ways. Mathematic grouping uses a local optimization method, and heuristic grouping is based on k-means. Specifically, two extensions are provided： the first one focuses on robustness, i.e., each user obtains search results even if some proxy servers fail; the second one focuses on benefit, i.e., each user can retrieve as many files as possible that may be of interest without increasing the sum. Extensive evaluations have been conducted on both a synthetic dataset and real query traces to verify the effectiveness of our strategies.

关键词： cloud computing cost efficiency load balancing robustness benefit

GA-Based Model Predictive Control of Semi-Active Landing Gear

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Chinese Journal of Aeronautics 2007年第1期20卷 47-54页

作者： wu Dong-su GU Hong-bin LIU Hui College of Civil Aviation Nanjing Universityy of Aeronautics and AstronauticsNanjing 210016 China

Semi-active landing gear can provide good performance of both landing impact and taxi situation, and has the ability for adapting to various ground conditions and operational conditions. A kind of Nonlinear Model Predictive Control algorithm （NMPC） for semi-active landing gears is developed in this paper. The NMPC algorithm uses Genetic Algorithm （GA） as the optimization technique and chooses damping performance of landing gear at touch down to be the optimization object. The valve＇s rate and magnitude limitations are also considered in the controller＇s design. A simulation model is built for the semi-active landing gear＇s damping process at touchdown. Drop tests are carried out on an experimental passive landing gear systerm to validate the parameters of the simulation model. The result of numerical simulation shows that the isolation of impact load at touchdown can be significantly improved compared to other control algorithms. The strongly nonlinear dynamics of semi-active landing gear coupled with control valve＇s rate and magnitude limitations are handled well with the proposed controller.

关键词： landing gear semi-active control: nonlinear model predictive control impact load genetic algorithm

A note on near-field site amplification effects of ground motion from a radially inhomogeneous valley

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Earthquake Engineering and Engineering Vibration 2018年第4期17卷 707-718页

作者： Zhang Ning Gao Yufeng wu Yongxin Zhang Fei Key Laboratory of Ministry of Education for Geomechanics and Embankment Engineering Hohai University College of Civil and Transportation Engineering Hohai University

To improve the understanding of the near-field soil and topographic amplification effects, an analytical solution by the authors for the scattering of plane SH waves by a radially inhomogeneous semi-cylindrical valley is extended to the case of a line source of cylindrical SH waves. Upon confirmation of its accuracy with past exact solutions for a homogeneous and an inhomogeneous semi-cylindrical valley under far-field plane SH waves, the extended solution is used to calculate the ground motion amplification factors for both the homogeneous and inhomogeneous valleys subjected to near-field waves. A comprehensive parametric study is conducted with respect to the location of the wave source, the dimensionless frequency of the incident waves, and the inhomogeneity degree of the covering soil layer. It is found that more amplifications and reductions of ground motions will occur within a certain range in and around the valley as the sources are located further. Consistent with the far-field case, it is confirmed that an increase of the degree of inhomogeneity of the covering soil layer generally amplifies the ground motions significantly.

关键词： elastic SH-waves wave scattering and diffraction ground motion amplification valley canyon

A NEW NUMERICAL WAVE FLUME COMBINING THE 0-1 TYPE BEM AND THE VOF METHOD

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Journal of Hydrodynamics 2012年第4期24卷 506-517页

作者： GUO Li-dong SUN Da-peng wu Hao State Key Laboratory of Coastal and Offshore Engineering Dalian University of TechnologyDalian 116024China

A new coupling numerical wave model, based on both the Boundary Element Method （BEM） and the Volume Of Fluid （VOF） method, is established by taking advantages of the both methods to solve the wave-structure interaction problems. In this model, the wave transformation in front of structures is calculated by the 0-1 type BEM, and the intense wave motions near the structures are calculated by the VOF method. In this paper, the characteristics of the BEM and the VOF method are discussed first, and then the coupling treatments are described in detail. In the end, the accuracy and the validity of the coupling model are examined by comparing the numerical results with experiment results and other numerical results available for the interactions between regular waves with a monolayer horizontal plate.

关键词： Boundary Element Method (BEM) Volume Of Fuid (VOF) method coupling numerical wave model horizontal plate