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Qualitative Analysis for Rheodynamic Model of Cardiac Pressure pulsations

Acta Mathematicae Applicatae Sinica 2004年第4期20卷 573-578页

作者： Zhi-congLiu Bei-yeFeng AcademyofMathematicsandSystemsSciences ChineseAcademyofSciencesBeijing100080China

In this paper, we give a rigorous mathematical and complete parameter analysis for the rheodynamic model of cardiac and obtain the conditions and parameter region for global existence and uniqueness of limit cycle and... 详细信息

关键词： Rheodynamic model cardiac pressure pulsations limit cycle

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Numerical Study of Pressure Pulsation of Centrifugal Pumps with the Compressible Mode

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Journal of Thermal Science 2019年第1期28卷 106-114页

作者： YANG Jun LIU Jun LIU Xiaohua XIE Tian School of Energy and Power Engineering University of Shanghai for Science and Technology School of Aeronautics and Astronautics Shanghai Jiao Tong University

The compressible effect of water is often neglected in the simulation of hydraulic machinery. However, based on experimental and numerical study, it is found that the compressibility of water could influence the magnitude of the pressure pulsation at some frequency in the pump. Therefore, in order to investigate the influence of water compressibility, compressible model is established by using Tait equation. The internal flow of centrifugal pump under different conditions is calculated by this model. The calculated results are compared with the incompressible results, and it is indicated that the compressibility of water has little effect on the performance parameters. But it affects the amplitude of pressure fluctuations at some discrete frequency, especially at the outlet of impeller and volute tongue where significant jet-wake and rotor/stator interaction appears respectively. Meanwhile, water compressibility makes greater influence on the flow pulsation under off-design condition. Therefore, it is necessary to consider the compressibility of working medium in the numerical simulation of unsteady flow in centrifugal pumps, especially in area with strong unsteady flow and at off-design condition.

关键词： water compressibility Tait equation unsteady flow pressure pulsations centrifugal pump

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Heat transfer in a tapered fluidized bed of biomass particles with pulsed gas flow

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Particuology 2019年第1期17卷 2-14页

作者： Dening Jia Xiaotao Bi C. Jim Lim Shahab Sokhansanj Atsushi Tsutsumi Department of Chemical and Biological Engineering The University of British Columbia2360 East MallVancouverBCV6T 1Z3Canada Environmental Sciences Division Oak Ridge National LaboratoryOak RidgeTN 37831USA Collaborative Research Center for Energy Engineering Institute of Industrial ScienceThe University of Tokyo4-6-1 KomabaMeguro-kuTokyo 153-8505Japan

Bed-to-surface heat transfer of pure biomass particles in a pulsed fluidized bed with a tapered bottom section was investigated. Three biomass species — Douglas fir, pine, and switchgrass — were studied under various operating conditions. Their heat transfer coefficients were found to be closely associated with hydrodynamics dominated by gas pulsations. A higher superficial gas velocity generally yielded better gas–solid contact and higher heat transfer rates. A moderately increasing pulsation frequency promoted convective heat transfer of particles but also reduced pulsation intensity, leading to undesired flow behaviours such as channelling and partial defluidization. The study of the pulsation duty cycle revealed that, for cohesive particles, a smaller duty cycle was preferred to generate powerful pulsations to break up inter-particle forces. Moreover, a duty cycle increase allowed higher gas throughput as long as a suitable fluidization was maintained. The addition of finer particles to a coarse fraction increased particle mobility, and subsequently heat transfer, which also explained the higher heat transfer coefficients of switchgrass as it contained more fines compared with fir and pine. Experimental results in the tapered bed were also compared with those of non-tapered geometry where a 10%–20% increase in heat transfer was observed.

关键词： Fluidized bed Gas pulsations Tapered column Heat transfer Biomass

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Detection of the Critical Duration of Different Types of Voltage Sags for Synchronous Machine Torque Oscillation

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Energy and Power Engineering 2012年第3期4卷 117-124页

作者： Jaber Alipoor Aref Doroudi Morteza Ghaseminezhad Department of Electrical Engineering Shahed University Tehran Iran

Voltage sages are classified in seven types that in each type, the voltage amplitude and angle of phase voltages are different. We demonstrated that voltage sag types have different effects on synchronous motor, especially on its torque pulsations. Torque pulsations are different in shape of oscillations and moreover, peak torque when voltage magnitude is restored has different correlation with sag duration, as sag type varies. By flux trajectory analysis, we mathematically extracted the critical durations for different types of voltage sags, in the case that the sag begins at the zero angle of the voltage wave. In order to observe the validity of the results, we simulated a synchronous motor subjected to different types of voltage sags. The simulation results confirmed the claim.

关键词： Flux Trajectory Analysis Power Quality Synchronous Motor Torque pulsations Voltage Sag

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