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Global frequency distributions of pulsations driven by sharp decrease of solar wind dynamic pressure

Science China Earth Sciences 2015年第12期58卷 2211-2219页

作者： wang zhiqiang Department of Space Science and Application College of Astronautics Nanjing University of Aeronautics and Astronautics

On 24 August 2005, an impulse of solar wind dynamic pressure(Psw) hit the magnetosphere. Using the high resolution geomagnetic field data from 15 ground stations and the data from Geotail and TC-1, we studied the geomagnetic pulsations at auroral latitudes driven by the sharp decrease of Psw at the trailing edge of the impulse. The results show that the sharp decrease of Psw can excite a global pulsation in the frequency range 4.3–11.6 m Hz. The pulsation has a reversal of polarization between two auroral latitude stations, a larger power spectral density(PSD) close to resonant latitude and increasing frequency with decreasing latitude. All these features indicate that the pulsations are associated with field line resonance(FLR). The fundamental resonant frequency(the peak frequency of PSD between 4.3 and 5.8 m Hz) is dependent on magnetic local time and is largest around magnetic local noon. This feature is due to the fact that the size of magnetospheric cavity is dependent on local time and smallest at noon. A second harmonic wave at about 10 m Hz is also observed, which is strongest in the daytime sector, and becomes heavily attenuated in the night sector. The comparison of the PSDs of the pulsations driven by sharp increase and sharp decrease of Psw shows that the frequency of pulsations is negatively proportional to the size of magnetopause. Since the FLR is excited by compressional cavity/waveguide waves, the above results indicate that the resonant frequency in the magnetospheric cavity/waveguide is controlled not only by solar wind parameters but also by magnetic local time of observation point.

关键词： solar wind-magnetosphere interactions plasma waves and instabilities magnetopause cusp boundary layers

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Exact Controllability for Nonautonomous First Order Quasilinear Hyperbolic Systems

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Chinese Annals of Mathematics,Series B 2006年第6期27卷 643-656页

作者： zhiqiang wang School of Mathematical Sciences Fudan University Shanghai 200433 China

By means of the theory on the semi-global C^1 solution to the mixed initialboundary value problem （IBVP） for first order quasilinear hyperbolic systems, we establish the exact controllability for general nonautonomo... 详细信息

关键词： Nonautonomous quasilinear hyperbolic system Mixed initial-boundaryvalue problem Semi-global C^1 solution Exact controllability

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On the Asymptotic Stability of Wave Equations Coupled by Velocities of Anti-symmetric Type

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Chinese Annals of Mathematics,Series B 2021年第6期42卷 813-832页

作者： Yan CUI zhiqiang wang Department of Mathematics Jinan UniversityGuangzhou 510632China School of Mathematical Sciences and Shanghai Key Laboratory for Contemporary Applied Mathematics Fudan UniversityShanghai 200433China

In this paper,the authors study the asymptotic stability of two wave equations coupled by velocities of anti-symmetric type via only one *** adopt the frequency domain method to prove that the system with smooth initial data is logarithmically stable,provided that the coupling domain and the damping domain intersect each ***,they show,by an example,that this geometric assumption of the intersection is necessary for 1-D case.

关键词： Wave equations Coupled by velocities Logarithmic stability

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Distribution Performance Analysis and Experimental Research on the Port Plate Pairs of Low Speed High Torque Seawater Hydraulic Motor

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Chinese Journal of Mechanical Engineering 2019年第6期32卷 206-218页

作者： zhiqiang wang Shaofeng Wu Dianrong Gao Shuncai wang School of Mechanical Engineering Hangzhou Dianzi UniversityHangzhou 310018China Zhejiang University Hangzhou 310058China cnCATS Faculty of Engineering and the EnvironmentUniversity of SouthamptonSouthamptonUK School of Mechanical Engineering Yanshan UniversityQinhuangdao 066004China

The current research of seawater hydraulic motor mainly focused on piston motor and vane motor, but seldom regarded low speed high torque seawater hydraulic motor. Low speed high torque seawater hydraulic motor as a kind of energy conversion device and actuator plays an important role in seawater hydraulic transmission system. However, the physical and chemical properties of seawater, such as low viscosity, high causticity and poor lubrication, result in numerous problems. In this paper, the flow distribution characteristics of port plate pairs for the seawater hydraulic motor are investigated, and the leakage flow and power loss models of port plate pairs are established. Numerical simulations are carried out to examine the effects of water film, inlet pressure and rotating speed on the pressure distribution and leakage flow. And the friction and wear tests of port plate pairs are also carried out. Moreover, the test system of the seawater hydraulic motor is constructed and the performance of prototype with no-load or loading is conducted. The results indicate that the clearance of port plate pairs and inlet pressure have a significant effect on distribution characteristics, but the effect of rotating speed is not very obvious. The experimental results show that the minimum error rate can be maintained within 0.3% by the proposed flow model and the counter materials of 316 L against carbon-fiber-reinforced polyetheretherketone(CFRPEEK) are suitable for the port plate pairs of seawater hydraulic motor. Finally, based on the seawater hydraulic experiment platform, the volumetric efficiency of no-load and loading are obtained that the maximum can achieve 94.71% and 90.14%, respectively. This research work may improve the flow distribution performance, lubrication and the friction and wear properties, enhance energy converting efficiency of port plate pair and provide theoretical and technical support for the design of highperformance water hydraulic components.

关键词： Seawater hydraulic motor Port plate pairs Leakage flow Clearance Numerical simulation Friction andwear

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From the editors:special issue announcement

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Earthquake Engineering and Engineering Vibration 2009年第2期8卷 251-261页

作者： wang zhiqiang George C. Lee Department of Bridge Engineering Tongji University Shanghai 200092 China Department of Civil Structural and Environmental Engineering University at Buffalo State University of New York USA

A comparative study of selected bridge damage due to the Wenchuan, Northridge, Loma Prieta and San Fernando earthquakes is described in this paper. Typical ground motion effects considered include large ground fault displacement, liquefaction, landslide, and strong ground shaking. Issues related to falling spans, inadequate detailing for structural ductility and complex bridge configurations are discussed within the context of the recent seismic design codes of China and the US. A significant lesson learned from the Great Wenchuan earthquake, far beyond the opportunities to improve the seismic design provisions for bridges, is articulated.

关键词： bridge damage Wenchuan earthquake Northridge earthquake Loma Prieta earthquake San Fernandoearthquake ground motion liquefaction landslide

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Improvement of the Subcooling Problem of Sodium Acetate Trihydrate by a Combination of Stirring or Internal Electric Field and Nucleating Agent

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Journal of Thermal Science 2024年第6期33卷 2235-2244页

作者： wang Chuang wang Suyaola LIU Pengcheng CHENG Xingxing wang zhiqiang School of Energy and Power Engineering Shandong UniversityJi'nan 250061China National Engineering Laboratory for Reducing Emissions from Coal Combustion Ji'nan 250061China

Energy storage devices are the hub of a multi-energy complementary distributed energy *** salts are the most suitable phase change material for energy storage devices,but subcooling is the main obstacle to their *** requires a driving force so the use of nucleating agents alone does not reduce subcooling to a very low *** address this issue,this paper first screened nucleating agents and then further reduced the subcooling of sodium acetate trihydrate in conjunction with stirring or direct *** effects of rotor mass,rotational speed,direct current voltage,and electrode material on nucleation were ***,the stability of the composite phase change material in the presence of simultaneous stirring and energization was *** results showed that the addition of 1.5%in weight of disodium hydrogen phosphate dodecahydrate to sodium acetate trihydrate can reduce the subcooling to about 2.3℃.Continued addition of stirring or electricity can reduce the subcooling of sodium acetate trihydrate to within 0.5℃ or even eliminate *** higher the momentum of the stirring,the better the improvement in subcooling,phase separation,and thermal *** higher the direct current voltage,the better the nucleation effect,but the electrode life will be *** silver electrode has the best nucleation *** new material was produced in the solution after 100 cycles in the presence of both stirring and direct *** melting point of the phase change material was increased by 0.2℃ and the latent heat value decreased by 1.8%,still with good *** trace of deionized water should be added to the phase change material in subsequent studies to compensate for the consumption ofwaterby theanodicelution.

关键词： phase change material sodium acetate trihydrate subcooling stirring internal electric field

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Operational optimization of copper flotation process based on the weighted Gaussian process regression and index-oriented adaptive differential evolution algorithm

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Chinese Journal of Chemical Engineering 2024年第2期66卷 167-179页

作者： zhiqiang wang Dakuo He Haotian Nie College of Information Science and Engineering Northeastern UniversityShenyang 110004China State Key Laboratory of Synthetical Automation for Process Industries Northeastern UniversityShenyang 110004China

Concentrate copper grade(CCG)is one of the important production indicators of copper flotation processes,and keeping the CCG at the set value is of great significance to the economic benefit of copper flotation industrial *** paper addresses the fluctuation problem of CCG through an operational optimization ***,a density-based affinity propagationalgorithm is proposed so that more ideal working condition categories can be obtained for the complex raw ore ***,a Bayesian network(BN)is applied to explore the relationship between the operational variables and the *** on the analysis results of BN,a weighted Gaussian process regression model is constructed to predict the CCG that a higher prediction accuracy can be *** ensure the predicted CCG is close to the set value with a smaller magnitude of the operation adjustments and a smaller uncertainty of the prediction results,an index-oriented adaptive differential evolution(IOADE)algorithm is proposed,and the convergence performance of IOADE is superior to the traditional differential evolution and adaptive differential evolution ***,the effectiveness and feasibility of the proposed methods are verified by the experiments on a copper flotation industrial process.

关键词： Weighted Gaussian process regression Index-oriented adaptive differential evolution Operational optimization Copper flotation process

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Research on prediction model of formation temperature of ammonium bisulfate in air preheater of coal-fired power plant

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Chinese Journal of Chemical Engineering 2022年第8期35卷 202-210页

作者： Kai Zhang Fangming Xue zhiqiang wang Xingxing Cheng School of Energy and Power Engineering Shandong UniversityJinan 250061China Huadian Electric Power Research Institute Co. Ltd.Hangzhou 310030China

Ammonium bisulfate(ABS)is a viscous compound produced by the escape NH_(3) in the NO reduction process and SO_(3) in the flue gas at a certain temperature,which can cause the ash corrosion of the air preheater in coal-fired power ***,it is essential to study the formation temperature of ABS to prevent the deposition of ABS in air *** this paper,the SO_(3) reaction kinetic model is used to analyze the SO_(3) generation process from coal combustion to the selective catalytic reduction(SCR)exit stage,and the kinetic model of NO reduction is used to analyze the NH_(3) escape process.A prediction model for calculating the ABS formation temperature based on the S content in coal and NO reduction parameters of the SCR is proposed,solving the difficulty of measuring SO_(3) concentration and NH_(3) concentration in the previous calculation equation of ABS formation *** the reliability of the model is verified by the actual data of the power *** the influence of S content in coal,NH_(3)/NO_(x) molar ratio,different NO_(x) concentrations at SCR inlet,and NO removal efficiency on the formation temperature of ABS are analyzed.

关键词： Air preheater Ammonium bisulfate ABS formation temperature Reaction kinetics

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Electrokinetic energy conversion of electro-magneto-hydro-dynamic nanofluids through a microannulus under the time-periodic excitation

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Applied Mathematics and Mechanics(English Edition) 2021年第7期42卷 1029-1046页

作者： Guangpu ZHAO Jiali ZHANG zhiqiang wang Yongjun JIAN College of Sciences Inner Mongolia University of TechnologyHohhot 010051China Transportation Institute Inner Mongolia UniversityHohhot 010021China School of Mathematical Science Inner Mongolia UniversityHohhot 010021China

In this work,the effects of externally applied axial pressure gradients and transverse magnetic fields on the electrokinetic energy conversion(EKEC)efficiency and the streaming potential of nanofluids through a microannulus are *** analytical solution for electro-magneto-hydro-dynamic(EMHD)flow is obtained under the condition of the Debye-Huuckel ***,Green’s function method is used to obtain the analytical solutions of the velocity *** result shows that the velocity distribution is characterized by the dimensionless frequency?,the Hartmann number Ha,the volume fraction of the nanoparticlesφ,the geometric radius ratio a,and the wallζpotential ratio ***,the effects of three kinds of periodic excitations are compared and *** results also show that the periodic excitation of the square waveform is more effective in increasing the streaming potential and the EKEC *** is worth noting that adjusting the wallζpotential ratio and the geometric radius ratio can affect the streaming potential and the EKEC efficiency.

关键词： electrokinetic energy conversion(EKEC)efficiency nanofluid streaming potential magnetic field time-periodic excitation

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Combined effect of the use of carbon fiber and seawater and the molecular structure on the tribological behavior of polymer materials

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Friction 2018年第2期6卷 183-194页

作者： zhiqiang wang Jing NI Dianrong GAO School of Mechanical Engineering Hangzhou Dianzi University State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang University College of Mechanical Engineering Yanshan University

The combined effect of the use of carbon fiber and seawater and the molecular structure on the tribological behavior of various polymer materials under natural seawater lubrication was investigated. After the investigation, the wear morphology of the contact surface was observed by a laser scanning confocal microscope, and the texture of the wear scars and tracks were presented in 3 D profiles. Moreover, the mechanism of mixed lubrication and wear resistance was analyzed. The results demonstrated that the friction coefficient of carbon fiber-reinforced polyetheretherketone(CFRPEEK) is the lowest and fluctuates at approximately 0.11. Moreover, the seven polymer materials in ascending order of friction coefficients are CFRPEEK, carbon fiber-reinforced polyamide-imide, polytetrafluoroethylene, polyoxymethylene, polyetheretherketone(PEEK), acrylonitrile butadiene styrene resin, and glass fiber–epoxy resin. More critically, the simultaneous incorporation of deposition, polymeric scrap, hydrophilic groups, and seawater resulted in a decrease in the friction and wear of polymer materials under seawater lubrication. This observation implies that a synergistic friction-reducing and wear-resistant effect exists between carbon fiber, seawater, and the molecular structure of PEEK. As a result, a highly effective polymer material was discovered, CFRPEEK, which has the lowest friction coefficient of 0.11 and lowest wear rate of 2 × 10^(–5) mm^3?(N?m)^(-1) among the polymer materials; this validates the selection of dual friction pairs for seawater hydraulic components.

关键词： friction coefficient wear molecular structure polymer materials seawater lubrication

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