Modelling of the pressure-velocity correlation in turbulence diffusion

Most current computations of trubulent flows with second-moment closure adopt the diffusion models which neglect the effect of pressure-velocity correlation. In the present paper the importance of this correlation effect is elucidated the neglect of this effect accounts for some major defects in the wide application of the second-moment closures. Through the relation between and , established by Lumley, we propose here a new turbulence diffusion model which takes into consideration the pressure effect. Applications of this new model in the computation of shearless turbulence mixing layer and plane and round-jet flows show that the spreading rate of these flows can be satisfactorily captured.     

面向远海岛礁群的双向物流网络规划

针对若干远海岛礁群系统封闭性的分布特点,将中心岛礁选址、各岛礁建设泊位数量和规模、仓库储存量、运输船型和数量以及航线设置、班期组织等作为规划内容,以整个运输网络系统总成本最低为原则,综合考虑了仓库存储理论,建立了兼顾“选址-库存-路径”的规划模型。结合所建模型特点,提出了双层并行搜索遗传算法,构建了以海上运输为基本交通方式的双向物流系统。最后,以我国南海为例进行建模并求解,采用不同算法并通过多组不同规模的算例进行演算比较,验证了所建模型和算法的有效性与合理性。     

Numerical modeling of chlorine concentration in water storage tanks

In this paper, we describe a numerical model to simulate the evolution in time of the hydrodynamics of water storage tanks, with particular emphasis on the time evolution of chlorine concentration. The mathematical model contains several ingredients particularly designed for this problem, namely, a boundary condition to model falling jets on free surfaces, an arbitrary Lagrangian–Eulerian formulation to account for the motion of the free surface because of demand and supply of water, and a coupling of the hydrodynamics with a convection–diffusion–reaction equation modeling the time evolution of chlorine. From the numerical point of view, the equations resulting from the mathematical model are approximated using a finite element formulation, with linear continuous interpolations on tetrahedra for all the unknowns. To make it possible, and also to be able to deal with convection‐dominated flows, a stabilized formulation is used. In order to capture the sharp gradients present in the chlorine concentration, particularly near the injection zone, a discontinuity capturing technique is employed. Copyright © 2015 John Wiley & Sons, Ltd.     

A puzzle of the radio-quiet quasar PG 1407+265: Are optical and X-ray emissions produced from a relativistic jet?

PG 1407+265 is a radio quiet quasar that has a relativistic jet.In this report,we show some peculiar properties of its optical and X-ray emissions,which indicate possible non-thermal origins produced from the jet.We use a simple synchrotron + synchrotron self Compton (SSC) model to fit the emissions with different ratios of energy densities between the magnetic field and electrons (η≡U B/U e),which predicts a different γ-ray luminosity.The First LAT AGN Catalog (1LAC) did not include PG 1407+265,which indic...     

Reinvestigation of the ν2 + 2ν3 subband in the overtone icosad of 12CH4 using cavity ring-down (CRD) spectroscopy of a supersonic jet expansion

We report a detailed reinvestigation of the ν₂?+?2ν₃ combination band of methane ¹²CH₄ centred at (7510.3378?±?0.003)?cm^?1 ((225.154263?±?0.0001)?THz) within the icosad of the overtone absorption. A new experimental setup is described, allowing us to carry out cw-laser cavity ring-down spectroscopy (cw-CRDS) at instrumental resolution in the MHz range in seeded supersonic jet expansions down to rotational temperature of 7?K compared to previous cw-CRDS measurements in our group achieving about 50?K in expansions of neat CH₄. We provide a careful re-analysis on the basis of our new experimental results for the Q and R branch transitions including data obtained between about 7 and 300?K under various conditions. We resolve previously observed discrepancies of assignments and are able to present a definitive assignment for lines involving angular momentum quantum numbers up to J?=?4. The analysis of relative intensities in spectra taken at rotational and effective translational temperatures between about 50?K and less than 10?K indicate conservation of nuclear spin symmetry upon supersonic jet expansion, in agreement with previous results using other techniques and covering other spectral ranges.     

Dynamics of plasma channel in a parallel-plate plasma gun

Lumped parameter models for describing dynamics of the plasma channel in a parallel-plate plasma gun are compared with the experimental results obtained from two plasma guns with different rail geometries. Comparison between the experiments and the numerical calculations reveals that the lumped parameter models can be utilized to describe the dynamic motion of the plasma channel quite well. Parametric study shows that minimizing the line inductance and increasing the charging voltage on a capacitor as well as minimizing the gas injection time for reducing the mass of the plasma channel are the key factors to increase the flow velocity of the plasma jet ejected from the plasma gun.     

Numerical simulations of negatively buoyant jets in an immiscible fluid using the Particle Finite Element Method

Negatively buoyant jets consist in a dense fluid injected vertically upward into a lighter ambient fluid. The numerical simulation of this kind of buoyancy‐driven flows is challenging as it involves multiple fluids with different physical properties. In the case of immiscible fluids, it requires, in addition, to track the motion of the interface between fluids and accurately represent the discontinuities of the flow variables. In this paper, we investigate numerically the injection of a negatively buoyant jet into a homogenous immiscible ambient fluid using the Particle Finite Element Method and compare the two‐dimensional numerical results with experiments on the injection of a jet of dyed water through a nozzle in the base of a cylindrical tank containing rapeseed oil. In both simulations and experiments, the fountain inlet flow velocity and nozzle diameter have been varied to cover a wide range of Froude Fr and Reynolds Re numbers ( 0.1 < Fr < 30, 8 < Re < 1350), reproducing both weak and strong laminar fountains. The flow behaviors observed for the different numerical simulations fit in the regime map based on the Re and Fr values of the experiments, and the maximum fountain height is in good agreement with the experimental observations, suggesting that particle finite element method is a useful tool for the study of immiscible two‐fluid systems. Copyright © 2011 John Wiley & Sons, Ltd.     

对“四舍六入五留双”修约规则的商榷*

数值修约是分析化学教学的重要内容。目前,主流分析化学教材均采用 “四舍六入五留双”数值修约规则。详细剖析了该规则中尾数与进舍条件的关系,指出“四舍六入五留双”修约规则中应采用“尾数的首位”而不是“尾数”设置进舍条件,否则存在逻辑错误。对比分析表明,“四舍六入五留双”以数字4、5和6为比较值设置的修约规则等价于GBT8170—2008国家标准中以数字5为比较值设置的进舍规则,但GBT8170—2008国家标准的进舍规则的逻辑、表述等优于“四舍六入五留双”规则。因此,建议分析化学教材采用GBT8170—2008国家标准规定的数值修约相关内容。     

Pulsed microwave-driven argon plasma jet with distinctive plume patterns resonantly excited by surface plasmon polaritons

Atmospheric lower-power pulsed microwave argon cold plasma jets are obtained by using coaxial transmission line resonators in ambient air.The plasma jet plumes are generated at the end of a metal wire placed in the middle of the dielectric tubes.The electromagnetic model analyses and simulation results suggest that the discharges are excited resonantly by the enhanced electric field of surface plasmon polaritons.Moreover,for conquering the defect of atmospheric argon filamentation discharges excited by 2.45-GHz of continued microwave,the distinctive patterns of the plasma jet plumes can be maintained by applying different gas flow rates of argon gas,frequencies of pulsed modulator,duty cycles of pulsed microwave,peak values of input microwave power,and even by using different materials of dielectric tubes.In addition,the emission spectrum,the plume temperature,and other plasma parameters are measured,which shows that the proposed pulsed microwave plasma jets can be adjusted for plasma biomedical applications.