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1.
Jin-yuan Qian Bu-zhan Liu Zhi-jiang Jin Jian-kai Wang Han Zhang An-le Lu 《浙江大学学报(A卷英文版)》2016,17(1):54-64
The pilot-control globe valve (PCGV) is a novel globe valve with a piston-type valve core and a small pilot valve. It can utilize a pressure difference to control the state of the main valve by the pilot valve. In this paper, a mathematical model of PCGV is established and a computational fluid dynamics (CFD) method is used to numerically simulate its flow and cavitation characteristics. Analysis of the pressure difference between the upside and downside of the valve core and comparison with similar previous work increase the reliability of the simulation. Then an analysis of flow and cavitation characteristics is carried out with three comparisons: a comparison between opened and closed states, a comparison between different inlet velocities, and a comparison between different valve core displacements. The results demonstrate that the vapor volume fraction reaches its peak point at the valve seat near the outlet tube, and that a higher inlet velocity or smaller valve core displacement can cause greater cavitation damage. This study can help further design work for optimization and engineering applications of PCGV. 相似文献
2.
In an effort to find the effect of mass transfer ,surface tesion and drag forces on the velocity distribution,the mathematical model of the velocity profile of a nascent hollow fiber during membrane formation in the air gap region was numerically simulated by using the Runge-Kutta method (fourth-order method).The effect of mass transfer on velocity distribution based on the complicated function(G(Ch^s))was presented and the dffects of a complicated function were studied in two cases:in the first case,G(Ch^s) was constant;in the second,G(Ch^s) was variable.The latter was done by varying with the concentration of solvent in a nascent hollow fiber through the air-gap region.One empirical equation was used to describe this change and the predected values had a better agreement with the experimental values.To verify the moedl hypotheses,hollow fiber membranes were spun from 20:80 polybenzimidazole/polyetherimide dopes with 25.6 wt％ solid in N,N-dimethylacetamide (DMAc) using water as the external and internal coagulants.Based on the experimental results of dry-jet wet-spinning process for the fabrication of hollow fiber membranes,it is found that the model calculated values were in a good agreement with the experimental values. 相似文献
3.
Nonlinear dynamics analysis of a new autonomous chaotic system 总被引：2，自引：0，他引：2
CHU Yan-dong LI Xian-feng ZHANG Jian-gang CHANG Ying-xiang 《浙江大学学报(A卷英文版)》2007,8(9):1408-1413
In this paper,a new nonlinear autonomous system introduced by Chlouverakis and Sprott is studied further,to present very rich and complex nonlinear dynamical behaviors. Some basic dynamical properties are studied either analytically or nu-merically,such as Poincaré map,Lyapunov exponents and Lyapunov dimension. Based on this flow,a new almost-Hamilton chaotic system with very high Lyapunov dimensions is constructed and investigated. Two new nonlinear autonomous systems can be changed into one another by adding or omitting some constant coefficients. 相似文献
4.
电动截止阀是流体输送的重要元件.阀的传统设计方法很少从流体角度对其流道进行设计,其流阻系数比较大,容易造成局部压力损失.流体介质通过阀口时,流动方向发生变化,可能产生诸如局部涡流、空化、水锤和死水区等水流现象及湍流脉动噪声,对阀体有很强的破坏性,降低阀的使用寿命.基于RAN-S方程组和RNG k-ε湍流模型,利用CFD技术对全开启状态下的电动截止阀的内流道进行三维的湍流数值模拟,获得其总压图、速度矢量图、湍动能强度图.通过数值模拟,可以直观地显示阀的内流道中流体的流动过程.改变进出口段流道的长度、曲率以及阀杆在流道中的布局等,进出口的压力差相对于未改进前减少30%左右,速度突变区域明显缩小,局部涡流现象消失,湍动能强度也降低了15%左右. 相似文献
5.
A method was presented to implement the detecting and tracking of moving targets through omnidirectional vision. The method
combined optical flow with particle filter arithmetic, in which optical flow field was used to detect and locate moving targets
and particle filter was used to track the detected moving objects. According to the circular image character of omnidirectional
vision, the calculation equation of optical flow field and the tracking arithmetic of particle filter were improved based
on the polar coordinates at the omnidirectional center. The edge of a randomly moving object could be detected by optical
flow field and was surrounded by a reference region in the particle filter. A dynamic motion model was established to predict
particle state. Histograms were used as the features in the reference region and candidate regions. The mutual information
(MI) and Gaussian function were combined to calculate particle weights. Finally, the state of tracked object was computed
by the total particle states with weights. Experiment results show that the proposed method could detect and track moving
objects with better real-time performance and accuracy.
Supported by Tianjin Higher Education Technology Development Foundation (No.20071308), Tianjin Natural Science Foundation
(06YFJMJC03600) and National Natural Science Foundation of China (No.60773073).
YANG Shuying, born in 1964, female, Dr, Prof. 相似文献
6.
A system dynamics approach to urban water demand forecasting was developed based on the analysis of urban water resources
system, which was characterized by multi-feedback and nonlinear interactions among system elements. As an example, Tianjin
water resources system dynamic model was set up to forecast water resources demand of the planning years. The practical verification
showed that the relative error was lower than 10%. Furthermore, through the comparison and analysis of the simulation results
under different development modes presented in this paper, the forecasting results of the water resources demand of Tianjin
was achieved based on sustainable utilization strategy of water resources.
Supported by National Natural Science Foundation of China (No.50578108), Doctoral Programs Foundation of Ministry of Education
of China (No.20050056016), National Key Program for Basic Research (“973” Program, No.2007CB407306-1), Science and Technology
Development Foundation of Tianjin (No.033113811 and No.05YFSYSF032), Educational Commission of Hebei Province (No.2008324)
and Tianjin Social Key Foundation (No.tjyy08-01-078).
ZHANG Hongwei, born in 1956, male, Dr. Prof. 相似文献
7.
1 IntroductionItiswellknownthatfluidflowsinsealsandbear ingsturnfromlaminarregimeintoturbulentonewhentheirReynoldsnumberbecomeshigherthanacriticalvalue .Theearliesttheoriesofhydrodynamiclubricationhavebeenbasedonthepresumptionofex istenceoflaminarflowregime .Inturbulentregime ,however ,thecharacteristicsofsealsandbearingsdif ferfromthepredictionsbytheoriessobased .Speciallubricationtheoriesbasedoncontemporaryturbulencemodelssincethelaterhalfof 190 0’swerethereforedevelopedtotaketheeffectsof… 相似文献
8.
Reaction thrust of water jet for conical nozzles 总被引：1，自引：0，他引：1
Clear knowledge on the reaction thrust of water jet is valuable for better design of water jet propulsion system. In
this paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry
as well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has a
direct proportional relationship with the product of the inlet pressure, the square of flow rate and two-thirds power exponent
of the input power. The results also indicate that the diameter of the cylinder column for the conical nozzle has great influence
on the reaction thrust characteristics. In addition, the best values of the half cone angle and the cylinder column length exist
to make the reaction thrust reach its maximum under the same inlet conditions． 相似文献
this paper, theoretical, numerical and experimental studies were carried out to investigate the effects of the nozzle geometry
as well as the inlet conditions on the reaction thrust of water jet. Comparison analyses reveal that the reaction thrust has a
direct proportional relationship with the product of the inlet pressure, the square of flow rate and two-thirds power exponent
of the input power. The results also indicate that the diameter of the cylinder column for the conical nozzle has great influence
on the reaction thrust characteristics. In addition, the best values of the half cone angle and the cylinder column length exist
to make the reaction thrust reach its maximum under the same inlet conditions． 相似文献
9.
The poppet valve is a fundamental component in fluid power systems. Under particular conditions, annoying “squeal” noises may be generated in hydraulic poppet valves. In the present study, the frequency spectrum of the squeal noise is obtained by analyzing the sampling data from the accelerometer mounted on the valve body. It is found that the flow velocity, pressure, and structural parameters have crucial effects on the properties of squeal noise, especially frequency. Larger valve chamber volume or lower backpressure leads to lower fundamental frequency of the squeal noise. An explanation for the squeal noise, as a result of Helmholtz resonance, is suggested and proved by experimental results. 相似文献
10.
A repulsive vortex-vortex interaction model was used to numerically study the melting transition of the two-dimensional vortex
system with Monte Carlo method. Then a δ-function-like peak in the specific heat was observed and the internal energy showed
a sharp drop at the melting temperature, which indicated that there exists a first-order melting transition at finite temperatures.
The Lindemann criterion was also investigated and valid, but different from previous simulation results.
Project supported by the Science and Technology Ministry of China (No. NKBRST-G19990646) and Zhejiang Provincial Natural Science
Foundation (No. 199031) 相似文献
11.
INTRODUCTION An Artificial Neural Network (ANN) is an in-formation-processing paradigm that is inspired by the way biological nervous systems, such as the brain, process information. It is composed of a large number of highly interconnected processing elements (neu-rons) working in unison to solve specific problems. In recent years, neural network has been widely applied in the field of engineering construction as a large dimensional nonlinear dynamic system, because of its support for … 相似文献
12.
Objective To explore how arylamine N-acetyltransferases (NATs) is related to cell apoptosis.
Methods NAT activity in apoptotic HepG2 cells was measured using high performance liquid chromatography (HPLC); the apoptosis rate
of HepG2 cells acted upon by an NAT inhibitor was measured using flow cytometry.
Results NAT activity was lowered in apoptotic HepG2 cells; apoptosis rate induced by camptothecin (CAM) increased after inhibition
of NAT activity in HepG2 cells.
Conclusion NAT can inhibit apoptosis in HepG2 cells.
Project supported by the National Natural Science Foundation of China (No. 30400591), the Science Foundation of Heilongjiang
Province, China (Nos. D2004-13 and D200505), and the Young Scientist Fund of Harbin City, China (No. 2004AFQXJ035) 相似文献
13.
卢义玉 《重庆大学学报(英文版)》2003,2(1)
~~00002RKRSr= (6) If 0tKt=, Eqs. (2),(3) and (4) change into the following equation that is applied to simulations using the MathCAD software. ddd(,,)dd1dxyygxyzzttt=== (7) where 11251(,,)()(1)gxyzABCyxaaaa=++-+, 2132131145678222124531678831(1),23(1)[(1sin],[3cos()] AyyByxxyxzCxyxyxyxzggaaaaaaaaaaaaagaaaa-------=--=++---+=+-- (8) 5g00pK6g0p… 相似文献
14.
Recently there has been an increasing interest in applying random walk based methods to recommender systems. We employ a Gaussian random field to model the top-N recommendation task as a semi-supervised learning problem, taking into account the degree of each node on the user-item bipartite graph, and induce an effective absorbing random walk （ARW） algorithm for the top-N recommendation task. Our random walk approach directly generates the top-N recommendations for individuals, rather than predicting the ratings of the recommendations. Experimental results on the two real data sets show that our random walk algorithm significantly outperforms the state-of-the-art random walk based personalized ranking algorithm as well as the popular item-based collaborative filtering method. 相似文献
15.
Exchange coupling and magnetization reversal mechanism in two series of Co_xNi_(1-x)/CoO(30 nm)(x=0.2 and 0.4)bilayers are studied by vector magnetometer.Two components of magnetization are measured parallel and perpendicular to the applied field.At low temperatures,coercivity H_c∝(t_(FM))~(-n),n=1.5 and 1.38 for x=0.2 and 0.4,respectively,in agreement with the random field model.At room temperature,the coercivity is nearly proportional to the inverse FM layer thickness.In addition to the exchange field and the coercivity,the characteristic of the magnetization reversal mechanism was found to change with temperature.At temperatures below 180 K,magnetization reversal process along the unidirectional axis is accompanied only by nucleation and pinning of domain wall while magnetization rotation is also involved at high temperatures. 相似文献
16.
Heat transfer between gas-solid multiphase flow and tubes occurs in many industry processes, such as circulating fluidized
bed process, pneumatic conveying process, chemical process, drying process, etc. This paper focuses on the influence of the
presence of particles on the heat transfer between a tube and gas-solid suspension. The presence of particles causes positive
enhancement of heat transfer in the case of high solid loading ratio, but heat transfer reduction has been found for in the
case of very low solid loading ratio (M
s of less than 0.05 kg/kg). A useful correlation incorporating solid loading ratio, particle size and flow Reynolds number
was derived from experimental data. In addition, thek-∈ two-equation model and the Fluctuation-Spectrum-Random-Trajectory Model (FSRT Model) are used to simulate the flow field
and heat transfer of the gasphase and the solid-phase, respectively. Through coupling of the two phases the model can predict
the local and total heat transfer characteristics of tube in gas-solid cross flow. For the total heat transfer enhancement
due to particles loading the model predictions agreed well with experimental data.
Project supported by National Natural Science Foundation for Distinguished Young Scholars (No. 50025618) 相似文献
17.
外电场作用下柔性模型水的分子动力学模拟 总被引：1，自引：0，他引：1
1 Introduction Water is the most common liquid in nature and it isalso i mportant in numerous chemical and biologicalprogresses . With the availability of computers , MonteCarlo (MC) and molecular dynamics (MD) si mulationshave beenintroduced and efforts have been devoted toexamining the microscopic structure and dynamicproperties of liquid water utilizing computer si mula-tions[1-8].It is known that liquid water is totally con-nected by random tetrahedral hydrogen-bonds net- work[1 ,2]. Ho… 相似文献
18.
Particle swarm optimization （PSO） is an efficient, robust and simple optimization algorithm. Most studies are mainly concentrated on better understanding of the standard PSO control parameters, such as acceleration coefficients, etc. In this paper, a more simple strategy of PSO algorithm called θ-PSO is proposed. In θ-PSO, an increment of phase angle vector replaces the increment of velocity vector and the positions are decided by the mapping of phase angles. Benchmark testing of nonlinear functions is described and the results show that the performance of θ-PSO is much more effective than that of the standard PSO. 相似文献
19.
n-soliton-like solutions of three non-isospectral equations, the non-isospectral mKdV equation, the non-isospectral sine-Gordon equation and the non-isospeetral nonlinear Schroedinger equation were obtained by using the Hirota method. 相似文献
20.
Xiao-li ZHAN ;Bi CHEN ;Qing-hua ZHANG ;Ling-min YI ;Bo JIANG ;Feng-qiu CHEN 《浙江大学学报(A卷英文版)》2008,9(9):1304-1308
A series of new amphiphilic poly[methyl（3,3,3-trifluoropropyl）siloxane]-b-poly（ethylene oxide） （PMTFPS-b-PEO） diblock copolymers with different ratios of hydrophobic segment to hydrophilic segment were prepared by coupling reactions of end-functlonal PMTFPS and PEO homopolymers. Copolymers were shown to be well defined and narrow molecular weight distribution （MWD） （1.07-1.3） by characterizations such as gel permeation chromatography （GPC） and ^1H-nudear magnetic resonance （^1H-NMR）. 相似文献