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Optimization of a global seventh-order dissipative compact finite-difference scheme by a genetic algorithm

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Applied Mathematics and Mechanics(English Edition) 2018年第11期39卷 1679-1690页

作者： yu LIN Yaming CHEN Chuanfu XU Xiaogang DENG College of Computer National University of Defense Technology College of Aerospace Science and Engineering National University of Defense Technology State Key Laboratory of High Performance Computing National University of Defense Technology

A global seventh-order dissipative compact finite-difference scheme is optimized in terms of time stability. the dissipative parameters appearing in the boundary closures are assumed to be different, resulting in an optimization problem with several parameters determined by applying a generic algorithm. the optimized schemes are analyzed carefully from the aspects of the eigenvalue distribution, the ε-pseudospectra, the short time behavior, and the Fourier analysis. Numerical experiments for the Euler equations are used to show the effectiveness of the final recommended scheme.

关键词： high-order dissipative compact finite-difference scheme genetic algorithm time stable

A numerical model for bird strike on sidewall structure of an aircraft nose

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Chinese Journal of Aeronautics 2014年第3期27卷 542-549页

作者： Liu Jun Li yulong Gao Xiaosheng yu Xiancheng School of Aeronautics Northwestern Polytechnical University Department of Mechanical Engineering The University of Akron

In order to examine the potential of using the coupled smooth particles hydrodynamic （SPH） and finite element （FE） method to predict the dynamic responses of aircraft structures in bird strike events, bird-strike tests on the sidewall structure of an aircraft nose are carried out and numerically simulated. the bird is modeled with SPH and described by the Murnaghan equation of state, while the structure is modeled with finite elements. A coupled SPH-FE method is developed to simulate the bird-strike tests and a numerical model is established using a commercial software PAM-CRASH. the bird model shows no signs of instability and correctly modeled the break-up of the bird into particles. Finally the dynamic response such as strains in the skin is simulated and compared with test results, and the simulated deformation and fracture process of the sidewall structure is compared with images recorded by a high speed camera. Good agreement between the simulation results and test data indicates that the coupled SPH-FE method can provide a very powerful tool in predicting the dynamic responses of aircraft structures in events of bird strike.

关键词： Bird strike Experiment Sidewall structure Simulation Smooth particles hydrodynamic (SPH) method

Static mechanical properties of hybrid RtM-made composite Ⅰ-and Ⅱ-beams under three-point flexure

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Chinese Journal of Aeronautics 2015年第3期28卷 903-913页

作者： Fu yu Xiong Junjiang Luo Chuyang yun Xinyao School of transportation Science and Engineering Beihang University

Abstract this paper deals with three-point flexure tests on hybrid I- and II-beams, made out of multi-layer carbon fiber/epoxy resin （including twill woven fabric CF3031/5284 and unidirectional cord fabric U3160/5284） reinforced composites, processed using the RtM （resin transfer molding） technique. Static bending properties were determined and failure initiation mechanism was deduced from experimental observations. Failure mode of the tested hybrid RtM-made I-beams can be reckoned to be characteristic of the delamination from the cutout edge within the web and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until local buckling within the curved webs around the conjunction fillet region. In contrast, as distinct from hybrid RtM I-beams subjected to three-point bending loading, hybrid RtM-made H-beams in three-point flexure tests experienced the resin debonding in the inverted triangular resin-rich zones and the debonding propagation along the interface between the inverted triangular resin-rich zone and the adjacent curved web until complete separation of the curved web from the flange. Progressive damage models （PDMs） were presented to predict fail- ure loads and process of hybrid RtM-made I- and N-beams under three-point flexure. Good cor- relation was achieved between experimental and numerical results.

关键词： Beam Composites Experiment Fabric Molding Simulation

Synthesis and Characterization of a Novel Silver-Substituted Calcium Phosphate Cement

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Journal of Materials Science & technology 2014年第7期30卷 686-691页

作者： tao yu Chengying Gao Jiandong Ye Ming Zhang Key Laboratory of Specially Functional Materials of Ministry of Education and School of Materials Science and Engineering South China University of Technology Interdisciplinary Division of Biomedical Engineering The Hong Kong Polytechnic University

Antibacterial materials play an important role in clinical application, and silver has been known to exhibit strong cytotoxicity towards a broad range of micro-organisms. In this work, the amorphous calcium phosphate with silver substitution （Ag-ACP） was synthesized by chemical precipitation method, and the valence of silver in ACP was adjusted by temperature. the processed Ag-ACP was combined with slightly acidic compounds to form new calcium phosphate cement （CPC）. Our results indicate that the valence of silver in CPC was adjusted successfully by chemical precipitation method and heat treatment. X-ray diffraction （XRD） and X-ray photoelectron spectroscopy （XPS） results demonstrated that silver ion in CPC-1 and CPC-2 existed in Ag3PO4, after heat treatment of 460℃, silver became more stable in CPC-3 and CPC-4. Silver in CPC-1 end CPC-2 exhibited better releasing property. After heat treatment at 460 ℃, the amount of silver ion released from CPC decreased significantly. Besides, the antibacterial ability of Ag-CPC was adjusted by changing the valence of silver in Ag-CPC. Depending on the low valence of silver and good silver release, CPC-1 and CPC-2 exhibited better antibacterial activity. We believe that this study will motivate the development and applications of antibacterial CPC in bone tissue regeneration.

关键词： Calcium phosphate Silver substitution Heat treatment Antimicrobial activity Escherichia coli

Prediction of stable high-pressure structures of tantalum nitride taN2

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Journal of Materials Science & technology 2019年第10期35卷 2297-2304页

作者： Wandong Xing Zijie Wei Rong yu Fanyan Meng Department of Physics University of Science and Technology BeijingBeijing Engineering Research Center of Detection and Application for Weak Magnetic FieldBeijing100083China School of Automation University of Science and Technology BeijingBeijing100083China National Center for Electron Microscopy in Beijing School of Materials Science and EngineeringKey Laboratory of Advanced Materials of Ministry of Education of ChinaState Key Laboratory of New Ceramics and Fine ProcessingTsinghua UniversityBeijing100084China

Structure searches based on a combination of first-principles calculations and a particle swarm optimization technique unravel two new stable high-pressure structures(C2/m and Cmce) for ta N2. the structural features, mechanical properties, formation enthalpies, electronic structure, and phase diagram of ta N2 are fully investigated. Being mechanically and dynamically stable, the two phases could be made metastable experimentally at ambient conditions.

关键词： Particle swarm optimization First-principles tantalum nitride Crystal structure High pressure

Slow light between two absorbing resonance in asymmetry double quantum dots

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Chinese Science Bulletin 2013年第20期58卷 2418-2422页

作者： yu ChunChao WANG tao Wuhan National Laboratory for Optoelectronics Huazhong University of Science and Technology College of Physical Science and technology Yangtze University

We demonstrate the slow light in double quantum dots (QDs) resonance dispersion material in theory. the slow factor, absorption, and bandwidth are greatly influenced by the energy difference of the two resonance energy. the bandwidth of this system is up to 60 GHz. the 20 ps input signal pulse is delayed by 180 ps (group index of approximately 55) relative to free-space propagation with little broadening in 1 mm dispersion material for the optical communication wavelength. the signal pulse delay can be tuned by the pump pulse.

关键词：双量子点共振能量吸收不对称脉冲延迟输入信号自由空间信号延迟

Quaternion-based Nonlinear trajectory tracking Control of a Quadrotor Unmanned Aerial Vehicle

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Chinese Journal of Mechanical Engineering 2017年第1期30卷 77-92页

作者： ZHA Changliu DING Xilun yu yushu WANG Xueqiang School of Mechanical Engineering and Automation Beihang UniversityBeijing 100191China

At present, most controllers of quadrotor unmanned aerial vehicles（UAVs） use Euler angles to express attitude. these controllers suffer a singularity problem when the pitch angle is near 90°, which limits the maneuverability of the UAV. to overcome this problem, based on the quatemion attitude representation, a 6 degree of freedom（DOF） nonlinear controller of a quadrotor UAV is designed using the trajectory linearization control（tLC） method. the overall controller contains a position sub-controller and an attitude sub-controller. the two controllers regulate the translational and rotational motion of the UAV, respectively. the controller is improved by using the commanded value instead of the nominal value as the input of the inner control loop. the performance of controller is tested by simulation before and after the improvement, the results show that the improved controller is better. the proposed controller is also tested via numerical simulation and real flights and is compared with the traditional controller based on Euler angles. the test results confirm the feasibility and the robustness of the proposed nonlinear controller. the proposed controller can successfully solve the singularity problem that usually occurs in the current attitude control of UAV and it is easy to be realized.

关键词： unmanned aerial vehicle quaternion nonlinear control trajectory linearization control singularity

Donor-acceptor covalent organic frameworks-confined ultrafine bimetallic Pt-based nanoclusters for enhanced photocatalytic H_(2)generation

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Nano Research 2024年第7期17卷 5835-5844页

作者： yu Liu Yawen Shi Hua Wang Shengbo Zhang Collaborative Innovation Center of Chemical Science and Engineering(tianjin) Key Laboratory for Green Chemical Technology of the Ministry of EducationSchool of Chemical Engineering and TechnologyTianjin UniversityTianjin 300350China School of Environmental Science and Engineering Tianjin Key Laboratory of Biomass/Wastes UtilizationTianjin UniversityTianjin 300350China

Photocatalytic hydrogen generation from hydrogen storage media is an effective and promising approach for the green hydrogen industry as well as for achieving carbon neutrality ***,the lower photocatalytic efficiency due to the limited light trapping capacity,low electron transfer rate,and severe aggregation of nanoparticles caused by high surface energy seriously restricts their practical ***,we constructed a series of donor–acceptor(D–A)type covalent organic frameworks to confine ultrafine bimetallic Pt-based nanoclusters for photocatalytic hydrogen generation from ammonia borane(AB)*** visible light irradiation at 20℃,PtCo_(2)@covalent organic framework(COF)showed the highest photocatalytic activity with a turnover frequency(tOF)of 486 min−*** and density functional theory(DFt)calculations reveal that the high catalytic activity is mainly attributed to the strong electronic interactions between D–A type COF and ultrafine PtCo_(2)***,the D–A type COF can significantly enhance the light-trapping ability by fine-tuning the electron-acceptor type in the framework,and accelerate the photogenerated electron transfer from D–A type COF to PtCo_(2)nanocluster,which promotes the adsorption and activation of H_(2)O and AB molecules and accelerates hydrogen ***,PtCo_(2)@COF also exhibited ultra-high durability due to the significantly enhanced resistance to nanocluster aggregation caused by the nanopore confinement effect of D–A type *** believe that this work will provide a theoretical guide for the rational design of efficient D–A COFbased catalysts for photocatalysis.

关键词： light trapping electron transfer donor-acceptor covalent organic frameworks(D-A COFs) bimetallic nanoclusters photocatalysis

Noncovalent conformational locks in organic semiconductors

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Science China Chemistry 2018年第11期61卷 1359-1367页

作者： Simiao yu Aidong Peng Shiming Zhang Hui Huang College of Materials Science and Opto-Electronic technology & Key Laboratory of Vacuum Physic University of Chinese Academy of Sciences Key Laboratory of Flexible Electronics (KLOFE) & Institute of Advanced Materials (IAM) Jiangsu National Synergetic Innovation Center for Advanced Materials (SICAM) Nanjing Tech University

Highly planar conformation is considered to be one of the most important properties for high performance organic semiconductors. Among all kinds strategies for designing highly performing materials, noncovalent conformational locks （NCLs） have been widely used to increase the planarity and rigidity for x-conjugated systems. this review summarizes π-conjugated small molecules and polymers by employing various NCLs for controlling molecular conformation in the past two years. the optoelectronic properties of the conjugated materials, together with their applications on organic field-effect transistors （OFEts） and organic photovoltaics （OPVs） are discussed. Besides, the outlook and challenges in this field are also presented. It is obvious that NCLs play an important role in the design and synthesis of high-performance organic semiconductors.

关键词： noncovalent conformational locks molecular conformation organic semiconductors