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Applied Mathematics and Mechanics(English Edition) 2021年第6期42卷 805-818页

作者： yunfei liu Zhaoye QINT Fulei CHU State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBejing 100084China

In this article, the nonlinear dynamic responses of sandwich functionally graded(FG) porous cylindrical shell embedded in elastic media are investigated. The shell studied here consists of three layers, of which the outer and inner skins are made of solid metal, while the core is FG porous metal foam. Partial differential equations are derived by utilizing the improved Donnell's nonlinear shell theory and Hamilton's principle. Afterwards, the Galerkin method is used to transform the governing equations into nonlinear ordinary differential equations, and an approximate analytical solution is obtained by using the multiple scales method. The effects of various system parameters,specifically, the radial load, core thickness, foam type, foam coefficient, structure damping,and Winkler-Pasternak foundation parameters on nonlinear internal resonance of the sandwich FG porous thin shells are evaluated.

关键词： nonlinear internal resonance sandwich functionally graded(FG)porous shell improved Donnell's nonlinear shell theory multiple scales method Galerkin method

Discriminative feature encoding for intrinsic image decomposition

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Computational Visual Media 2023年第3期9卷 597-618页

作者： Zongji Wang yunfei liu Feng Lu Key Laboratory of Network Information System Technology(NIST) Aerospace Information Research InstituteChinese Academy of SciencesBeijing 100190China State Key Laboratory of Virtual Reality Technology and Systems School of Computer Science and EngineeringBeihang UniversityBeijing 100191China Peng Cheng Laboratory Shenzhen 518000China

Intrinsic image decomposition is an important and long-standing computer vision *** an input image,recovering the physical scene properties is *** physically motivated priors have been used to restrict the solution space of the optimization problem for intrinsic image *** work takes advantage of deep learning,and shows that it can solve this challenging computer vision problem with high *** focus lies in the feature encoding phase to extract discriminative features for different intrinsic layers from an input *** achieve this goal,we explore the distinctive characteristics of different intrinsic components in the high-dimensional feature embedding *** define feature distribution divergence to efficiently separate the feature vectors of different intrinsic *** feature distributions are also constrained to fit the real ones through a feature distribution *** addition,a data refinement approach is provided to remove data inconsistency from the Sintel dataset,making it more suitable for intrinsic image *** method is also extended to intrinsic video decomposition based on pixel-wise correspondences between adjacent *** results indicate that our proposed network structure can outperform the existing state-of-the-art.

关键词： intrinsic image decomposition deep learning feature distribution data refinement

Analysis of Wear Mechanism and Influence Factors of Drum Segment of Hot Rolling Coiler

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Chinese Journal of Mechanical Engineering 2013年第2期26卷 351-355页

作者： ZHANG Jian PENG Yan liu Hongmin liu yunfei National Engieering Research Center for Equipment and Technology of Cold Rolling Strip Yanshan University State Key Laboratory of Metastable Materials Science and Technology Yanshan University

Because the work environment of segment is complex, and the wear failures usually happen, the wear mechanism corresponding to the load is a key factor for the solution of this problem. At present, many researchers have investigated the failure of segment, but have not taken into account the compositive influences of matching and coiling process. To investigate the wear failure of the drum segment of the hot rolling coiler, the MMU-5G abrasion tester is applied to simulate the wear behavior under different temperatures, different loads and different stages, and the friction coefficients and wear rates are acquired. Scanning electron microscopy（SEM） is used to observe the micro-morphology of worn surface, X-ray energy dispersive spectroscopy（EDS） is used to analyze the chemical composition of worn surface, finally the wear mechanism of segment in working process is judged and the influence regulars of the environmental factors on the material wear behaviors are found. The test and analysis results show that under certain load, the wear of the segment changes into oxidation wear from abrasive wear step by step with the temperature increases, and the wear degree reduces; under certain temperature, the main wear mechanism of segment changes into spalling wear from abrasive wear with the load increases, and the wear degree slightly increases. The proposed research provides a theoretical foundation and a practical reference for optimizing the wear behavior and extending the working life of segment.

关键词： friction coefficient wear rate micro-morphology wear mechanism wear resistance

Nonlinear free vibration of piezoelectric cylindrical nanoshells

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Applied Mathematics and Mechanics(English Edition) 2019年第5期40卷 601-620页

作者： Yanqing WANG yunfei liu J.W.ZU Department of Mechanics Northeastern University Key Laboratory of Ministry of Education on Safe Mining of Deep Metal Mines Northeastern University Schaefer School of Engineering and Science Stevens Institute of Technology

The nonlinear vibration characteristics of the piezoelectric circular cylindrical nanoshells resting on an elastic foundation are analyzed. The small scale effect and thermo-electro-mechanical loading are taken into account. Based on the nonlocal elasticity theory and Donnell's nonlinear shell theory, the nonlinear governing equations and the corresponding boundary conditions are derived by employing Hamilton's principle. Then,the Galerkin method is used to transform the governing equations into a set of ordinary differential equations, and subsequently, the multiple-scale method is used to obtain an approximate analytical solution. Finally, an extensive parametric study is conducted to examine the effects of the nonlocal parameter, the external electric potential, the temperature rise, and the Winkler-Pasternak foundation parameters on the nonlinear vibration characteristics of circular cylindrical piezoelectric nanoshells.

关键词： piezoelectric cylindrical nanoshell nonlinear vibration Donnell's nonlinear shell theory nonlocal elasticity theory multiple-scale method size effect

Detoxification and concentration of corn stover hydrolysate and its fermentation for ethanol production

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Frontiers of Chemical Science and Engineering 2019年第1期13卷 140-151页

作者： Qing Li Yingjie Qin yunfei liu Jianjun liu Qing liu Pingli Li Liqiang liu School of Chemical Engineering and Technology Tianjin University Tianjin 300072 China Chembrane Engineering & Technology Inc. Tianjin 300308 China

Environmental and energy concerns have increased interest in renewable energy sources, particularly biofuels. Thus the fermentation of glucose from sulfuric acid-hydrolyzed corn stover for the production of bioethanol has been explored using a combined acid retardation and continuous-effect membrane distillation treatment process. This process resulted in the separation of the sugars and acids from the acid-catalyzed hydrolysate, the removal of most of the fermentation inhibitors from the hydrolysate and the concentration of the detoxified hydrolysate. The recovery rate of glucose from the sugar-acid mixture using acid retardation was greater than 99.12% and the sulfuric acid was completely recovered from the hydrolysate. When the treated com stover hydrolysate, containing 100 g/L glucose, was used as a carbon source, 43.06 g/L of ethanol was produced with a productivity of 1.79 g/(L· h) and a yield of 86.31 %, In the control experiment, where glucose was used as the carbon source these values were 1.97 g/(L·h) and 93.10% respectively. Thus the integration of acid retardation and a continuous-effect membrane distillation process are effective for the production of fuel ethanol from com stover.

关键词： com stover hydrolysate acid retardation continuous-effect membrane distillation ethanol fermentation

Nonlinear characteristic investigation of magnetorheological damper-rotor system with local nonlinearity

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Chinese Journal of Aeronautics 2023年第2期36卷 111-126页

作者： Jun WANG yunfei liu Zhaoye QIN Liang MA Fulei CHU State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China College of Aeronautical Engineering Civil Aviation University of ChinaTianjin 300300China

Magnetorheological(MR)dampers show superior performance in reducing rotor vibration,but their high nonlinearity will cause nonsynchronous response,resulting in fatigue and instability of ***,we are devoted to the investigation of the nonlinear characteristics of MR damper mounted on a flexible ***,Reynolds equations with bilinear constitutive equations of MR fluid are employed to derive nonlinear oil film ***,the Finite Element(FE)model of rotor system is developed,where the local nonlinear support forces produced by MR damper and its coupling effects with the rotor are considered.A hybrid numerical method is proposed to solve the nonlinear FE motion equations of the MR damper-rotor *** validate the proposed model,a rotor test bench with two dual-coil MR dampers is constructed,upon which experimental studies on the dynamic characteristics of MR damper-rotor system are carried *** effects of different system parameters,including rotational speed,excitation current and amount of unbalance,on nonlinear dynamic behaviors of MR damper-rotor system are *** results show that the system may appear chaos,jumping,and other complex nonlinear phenomena,and the level of the nonlinearity can be effectively alleviated by applying suitable excitation current and oil supply pressure.

关键词： Hybrid numerical method Local nonlinearity Magnetorheological damper Nonlinear vibration Rotor system

Multiple internal resonances of rotating composite cylindrical shells under varying temperature fields

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Applied Mathematics and Mechanics(English Edition) 2022年第10期43卷 1543-1554页

作者： yunfei liu Jun WANG Jiaxin HU Zhaoye QIN Fulei CHU State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China

Composite cylindrical shells,as key components,are widely employed in large rotating ***,due to the frequency bifurcations and dense frequency spectra caused by rotation,the nonlinear vibration usually has the behavior of complex multiple internal *** addition,the varying temperature fields make the responses of the system further difficult to ***,the multiple internal resonances of composite cylindrical shells with porosities induced by rotation with varying temperature fields are studied in this *** different types of the temperature fields,the Coriolis forces,and the centrifugal force are considered *** Hamilton principle and the modified Donnell nonlinear shell theory are used to obtain the equilibrium equations of the system,which are transformed into the ordinary differential equations(ODEs)by the multi-mode Galerkin ***,the pseudo-arclength continuation method,which can identify the regions of instability,is introduced to obtain the numerical *** detailed parametric analysis of the rotating composite shells is *** internal resonances caused by the interaction between backward and forward wave modes and the energy transfer phenomenon are ***,the nonlinear amplitude-frequency response curves are different under different temperature fields.

关键词： multiple internal resonances rotation effect nonlinear temperature variation multi-mode Galerkin technique pseudo-arclength continuation method coupled effect

Transient state analysis of a rub-impact rotor system during maneuvering flight

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Chinese Journal of Aeronautics 2024年第7期37卷 236-251页

作者： Jun WANG yunfei liu Zhaoye QIN Liang MA Fulei CHU Beijing Key Laboratory of Health Monitoring and Self-Recovery for High-End Machinery Equipment Beijing University of Chemical TechnologyBeijing 100029China State Key Laboratory of Tribology Department of Mechanical EngineeringTsinghua UniversityBeijing 100084China College of Aeronautical Engineering Civil Aviation University of ChinaTianjin 300300China

Maneuvering flight substantially affects the dynamic behavior of rotors;particularly,such flight may cause rubbing between a rotor and stator,which is one of the most serious damages in aircraft *** this paper,a nonlinear dynamic model for describing the dynamic characteristics of a rub-impact rotor system during maneuvering flight is established based on the Lagrange ***,numerical simulations employing the Newmark method are performed,delving into the detailed discussion of the influence of parameters such as rotational speed and maneuvering flight on the transient and steady-state responses of the rotor *** effect mechanism of maneuver load and its coupling with rub impact is *** results show that the impact response induced by maneuvering flight is more obvious in the subcritical state than in the supercritical *** additional stiffness and damping are also induced;in particular,the additional damping has a coupling ***,the rub impact imposes an additional constraint on the rotor system,thereby weakening the influence of the maneuver load and becoming the major factor that determines the dynamic behavior of the rotor system at high speeds.

关键词： Maneuvering flight Rub impact Rotor system Dynamic response Impact response

Maximum Data Collection Rate in Rechargeable Wireless Sensor Networks with Multiple Sinks

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China Communications 2016年第2期13卷 95-108页

作者： GAO Demin LIN Haifeng liu yunfei WU Guoxin College of Information Science and Technology Nanjing Forestry University School of Computer Science and Engineering Southeast University

In rechargeable wireless sensor networks, a sensor cannot be always benefi cial to conserve energy when a network can harvest excessive energy from the environment due to its energy replenished continually and limited energy storage capacity. Therefore, surplus energy of a node can be utilized for strengthening packet delivery efficiency and improving data collection rate. In this work, we propose an algorithm to compute an upper data generation rate that maximizes it as an optimization problem for a network with multiple sinks, which is formulated as a linear programming problem. Subsequently, a dual problem by introducing Lagrange multipliers is constructed, and subgradient algorithms are used to solve it in a distributed manner. The resulting algorithms are guaranteed to converge to an optimal data generation rate, which are illustrated by an example in which an optimum data generation rate is computed for a network of randomly distributed nodes. Through extensive simulation and experiments, we demonstrate our algorithm is efficient to maximize data collection rate in rechargeable wireless sensor networks.

关键词： wireless sensor networks maximumdata collection rate linear programming rechargeable-WSNs

Tunable Luminescence Properties and Elucidating the Electronic Structures of Single-Phase Spherical BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)Phosphors for Warm-White-Lighting

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Journal of Renewable Materials 2022年第2期10卷 431-451页

作者： Zun Bi Ke Jia yunfei liu Yinong Lyu State Key Laboratory of Materials–Orient Chemical Engineering College of Materials Science and EngineeringNanjing Tech UniversityNanjingChina Jiangsu National Synergetic Innovation Center for Advanced Materials(SICAM) NanjingChina Jiangsu Collaborative Innovation Center for Advanced Inorganic Function Composites NanjingChina

A series of uniform single-phase spherical BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)phosphors were prepared via a microwave hydrothermal method by using trisodium citrate dehydrate as *** phase structure,morphology and photoluminescence properties were measured by powder X-ray diffraction,scanning electron microscope and fluorescence spectrometer,*** results show that uniform spherical microcrystals with diameters in the range of 2–4μm are *** the phase and morphology of samples are not significantly changed by doping rare earth(RE^(3+))*** the excitation wavelength of 356 and 365 nm,the samples BaWO 4:0.03Dy^(3+),yTm^(3+)can emit cold white *** order to lower the correlated color temperature(CCT)to get a warm white light,the Eu^(3+)ions were doped into BaWO 4:0.03Dy^(3+),0.01Tm^(3+).Especially,under the excitation of 365 nm,BaWO 4:0.03Dy^(3+),0.01Tm^(3+),0.03Eu^(3+)phosphor shew a bright warm white light with color coordi-nate of(0.4013,0.3629)and CCT of 3288 ***,in the BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)phosphors,the energy transfer mechanism among Dy^(3+),Tm^(3+)and Eu^(3+)ions have been discussed and the change of electron structures have been calculated by first-principles *** results shew that the uniform single-phase spherical BaWO 4:Dy^(3+),Tm^(3+),Eu^(3+)phosphors could be favorable candidates in warm white LEDs.

关键词： Barium tungstate microwave hydrothermal method spherical warm white lighting electron structures