Numerical anatomy of lock-release gravity current

IntroductionGravity currents, which are primarily horizonta1 flows and generated by a density differenceof only a few percent, are recognzed by rnore and more scientists fqr its importance in envi-ronmental and industrial flo.s[i]. NIany interesting'fiows such as sea water intrusion, turbiditycurrents. sandstorms, avalanches and pollutant outfalls can be tegarded as gravity currents:.. ~ l'Lock.release gravity current, the most typical gravit1' current. is considered in this paper, as'a conti…     

The study and applications of photochemical-dynamical gravity wave model Ⅰ--Model description

A two-dimensional, nonlinear, compressible, diabatic, nonhydrostatic photochemical- dynamical gravity wave model has been advanced. The model includes diabetic process produced by photochemistry and the effect of gravity wave on atmospheric chemical species. In the horizontal direction, the pseudospectral method is used. The finite difference approximations are used in vertical direction z and time t. The FICE method is used to solve the model. The model results on small amplitude fluctuation are very close to those of linear theory, which demonstrates the correctness of the model.     

四方主体参与下的环境规制演化博弈分析

环境污染问题严重阻碍了我国经济和社会的发展,我国当下的环境治理逐步形成多主体治理模式。本文将环境治理中的四个主要相关主体“中央政府-地方政府-企业-公众”置于统一框架下,建立了四方演化博弈模型,并利用数值仿真模拟参数变化对博弈系统不同主体稳定策略的影响,得到以下结论:(1)四方演化博弈系统的16个纯策略均衡点中,共有8个条件稳定点,其余8个均衡点在任何条件下都不稳定。其中8个条件稳定点代表着我国环境治理中各利益相关主体可能呈现的策略均衡,策略集中某策略的相对净收益决定了相关主体的策略选择。(2)通过数值仿真分析发现,增大中央政府对地方政府消极执行的处罚、增大中央政府转移支付和增大中央政府对地方政府消极执行的追加处罚不仅能够提升地方政府的环保执法力度,而且可以提高企业减排积极性。提高环境规制标准、增大对企业非法排污的处罚,对地方政府、企业和公众的策略选择都会产生影响,可以使系统更快向“中央政府不严格监管、地方政府积极执行、企业合法排污、公众不举报”的理想稳定状态演化,但提高环境规制标准的效果会略优于加大对企业处罚。地方政府增大企业治污补贴短期内可有利于实现经济的可持续发展,但过高的企业治污补贴将不利于博弈系统达到理想稳定状态,是一种非长效的环境治理模式。提高公众举报奖励可以促使企业合法排污,并在一定程度上加快实现博弈系统的理想稳定状态。最后,分别从中央政府、地方政府和公众角度提出了环境治理的相关建议。     

Simulation of suspension gravity currents with different initial aspect ratio and layout of turbidity fence

A three-dimensional (3D) numerical model, using large eddy simulation (LES), is developed for simulating the motion of suspension gravity currents. The suitable values of model parameters are determined using the existing experimental data of a two-dimensional (2D) suspension (a mixture composed of water and glass bead particles) cloud. The simulated gravity current with different initial aspect ratio (length/breadth) of the suspension is compared with the reported data of 3D laboratory experiments to investigate the effect of initial aspect ratio on the flow characteristics and the diffusion of turbidity under the presence of a turbidity fence. The comparison of simulated results of such main flow characteristics as front height, front propagation velocity and particle deposition with the experimental data reveals that the model is capable of simulating the complex behavior of the 3D suspension gravity currents to a reasonably good accuracy under complex conditions.     

T型管中冷热流体混合过程热波动大涡模拟

在FLUENT平台上,运用大涡模拟湍流模型及Smagorinsky-Lilly亚格子模型,对T型混合结构中的温度波动进行了模拟．获得了分别用于描述时均温度和温度波动强度的无量纲时均温度和无量纲均方根温度．分析了用于热疲劳分析和生命周期评价关键参数,即温度波动的功率谱密度函数．对不同条件下的混合过程进行了模拟,分析不同Reynolds数Re和Richardson数Ri对混合过程和热波动的影响     

Gravity and Lorentz Force

The relativistic covariant equations are obtained for the relativistic Newton gravity law proposed by Poincaré. These equations are solved for the case where the mass of one gravitating body is equal to zero.     

Numerical simulation of discontinuous waves propagating over a dry bed

A numerical algorithm is proposed for simulating the propagation of discontinuous waves over a dry bed governed by the shallow water equations in the first approximation. The algorithm is based on a modified conservation law of total momentum that takes into account the concentrated momentum loss associated with the formation of local eddy structures within the framework of the long-wave approximation. The modified conservation law involves a heuristic parameter that is chosen so as to agree with laboratory experiments. Numerical results are presented for the formation, propagation, and transformation of a discontinuous wave arising in a complete or partial (in the planned case) collapse of a dam over a bed with a horizontal or sloping bottom or a bottom with a local obstacle in the tailwater area.     

微下拉法YAG晶体生长数值模拟

对微下拉法生长YAG晶体进行包括感应加热在内的全局数值模拟,其耦合了感应加热、气体与熔体对流以及固液气三相的热输运,熔体对流同时考虑浮力与表面张力作用.为统一使用有限体积法离散控制方程,采用复函数法求解电磁场,与流函数法对比验证程序正确性.分析整个生长炉内的温度和流场（包括气体和熔体）分布,并针对固液交界面区域温度梯度较小的情况,改进后热器材料,为微下拉法晶体生长炉结构设计提供参考.     

昆虫振翅飞行的数值模拟

在非惯性参考系下对昆虫振翅扰动的二维非定常流场进行了数值模拟,避免了计算中的移动边界困难,从而缩短了计算时间,模型具有3个自由度,可以模拟任意已知的翅的平面运动．通过模拟相对复杂的自然界昆虫的振翅运动,研究昆虫是如何控制飞行．计算结果表明,有2个参数可能被昆虫用来控制飞行：翅平动和转动间的相位差以及垂直于平均振翅平面方向的横向振幅．     

通过求解输运方程计算壁面距离

壁面距离在当代湍流模化中仍然扮演着关键角色,然而苦于遍历计算壁面距离的高昂代价,该文考虑了求解偏微分方程的途径．基于Eikonal方程构造出类Euler形式的输运方程,这样,可以直接利用求解Euler和Navier-Stokes方程的CFD程序使用的高效数值格式和部分代码．基于北航的MI-CFD(CFD for missles)数值平台,详尽地介绍了该输运方程在直角坐标下的求解过程．使用隐式LUSGS时间推进和迎风空间离散,发现该方程具有鲁棒快速的收敛特性．为了保证精度,网格度量系数必须也迎风插值计算．讨论了初始条件和边界条件的特殊处理．成功应用该壁面距离求解方法计算了几个含1-1对应网格和重叠网格的复杂外形．     

180°弯曲方管牛顿流体及一种非牛顿流体湍性流动的数值模拟

运用湍流k-ε模式及实测壁面函数分别模拟牛顿流体(清水)及一种非牛顿流体(聚合物稀薄减阻溶液)流经180°弯曲方管的湍性流动,取得与实测速度分布吻合较好的结果.对于湍流模式对存在大涡的复杂流动的适应性,根据计算和试验结果进行了分析和讨论.     

Shock-induced ignition of thermally sensitive explosives

The process of planar detonation ignition, induced by a constant-velocitypiston or equivalently by a shock reflected from a stationarywall, is investigated using high-resolution one-dimensionalnumerical simulations. The standard one-step model with Arrheniuskinetics, which models thermally sensitive explosives, is employed.Emphasis is on comparing and contrasting the results of thefinite activation temperature simulations with high activationtemperature asymptotic predictions and previous simulations.During the induction phase, it is shown that the asymptoticresults give qualitatively good predictions. However, for parametersrepresentative of gaseous explosives, subsequent to thermalrunaway at the piston and the formation of a reaction wave,the high activation temperature asymptotic theory is qualitativelyincorrect for moderately high activation temperatures. It isshown that the results are very sensitive to the value of theactivation temperature, especially the distance from the pistonat which a secondary shock forms and the degree of unsteadinessin the reaction wave which moves away from the piston. The dependenceof the ignition evolution on the other parameters (initial shockMach number, heat of reaction and polytropic index) is alsoinvestigated. It is shown that qualitative predictions regardingthe dependence of the ignition evolution on each of the parameterscan be elucidated from finite activation temperature homogeneousexplosion calculations together with the high activation temperatureasymptotic shock ignition results. It is found that for sufficientlystrong initiating shocks the ignition evolution is qualitativelydifferent from cases studied previously in that no secondaryshock forms. For a high polytropic index, corresponding to asimple equation of state model for condensed phase explosives,the results are in much better qualitative agreement with theasymptotic theory.     

激光传输孤波初态的数值模拟

本文利用有限元的方法求解 1 +3D维激光传输初态下的非线性 Schrodinger方程     

Three-dimensional numerical simulation of the plasma plume from a stationary plasma thruster

A numerical method is proposed for simulating the low-density plasma plume exhausted from a stationary plasma thruster in a three-dimensional setting. In contrast to the axisymmetric approximation, the problem is formulated so as to determine the effect of the backflow on the upstream region and the thruster walls, which are of finite size. The numerical method is a generalization of rarefied gas numerical methods to the case when the force field is not specified analytically. The method takes into account the delta-function character of the boundary ion distribution function and the considerable difference between the velocity scales of ions and neutral atoms, which transform into each other. Numerical results are presented that demonstrate the effect of some factors on the plasma plume.     

基于盲数理论和随机模拟的河流水环境容量计算

针对水环境系统的不确定性,将延拓盲数引入到水环境容量计算模型中,并运用随机模拟方法对盲参数进行模拟,把盲数之间的运算转化为普通实数之间的运算,从而建立了水环境容量的延拓盲数与随机模拟的耦合模型.经实例研究,得到研究对象的水环境容量随机模拟分布以及在不同保证率下的水环境容量值,为研究对象当地的水环境规划和保护提供丰富可靠的依据.     

K－ε模型在复杂管流中的模拟计算

本文对复杂管流中的湍流问题采用了k-ε模型进行模拟计算.对于复杂边界问题采用了阶梯型网格近似,取得了较好的结果.文中给出了两例复杂管流的计算算例,说明了K-ε模型具有很强的适应性和稳定性.     

基于Schwarz-Christoffel变换的非圆截面血管流场分布研究

应用Schwarz-Christoffel(S-C)变换方法,实现从复平面单位圆到多边形区域的共形映射,结合圆形管道下完全发展脉动流的Womersley算法理论,建立了基于S-C映射的非圆入口截面下的Womersley速度边界模型.在边界模型建立的基础上,应用计算流体力学方法,对基于生理真实的人体肺动脉二级分支血管在一个心动周期内的血流流动情况进行了数值模拟,并与通过外接圆管法设定入口速度边界条件得到的流场模拟结果进行了对比分析.分析结果表明,两者的模拟结果高度一致,但考虑到模拟效率和数值模拟结果的确定性,基于S-C映射的Womersley速度边界模型优于外接圆管方法,对于血管血流动力学的模拟研究更具有现实意义.     

滩海地区运移聚集的精细数值模拟和分析

对滩海地区三层油资源运移聚集进行高精度精细平行数值模拟,提出数学模型和精细平行算子分裂隐式迭代格式,设计了并行计算程序,提出了并行计算的信息传递和交替方向网格剖分方法. 并对不同的CPU组合进行并行计算和分析,对滩海地区数值模拟结果和实际情况吻合.对模型问题进行数值分析,得到最佳阶误差估计,成功地解决了这一困难问题．