Effect of shear equilibrium flow in Tokamak plasma on resistive wall modes

A code named LARWM with non-ideal magnetohydrodynamic equations in cylindrical model is used to describe the instability in Tokamak plasma surrounded by a conducting wall with finite resistivity. We mainly take three factors related to the shear equilibrium plasma flow into consideration to study the stabilizing effect of the shear flow on the resistive wall modes （RWMs）. The three factors are the velocity amplitude of flow, the shear rate of flow on plasma surface, and the inertial energy of equilibrium plasma flow. In addition, a local shear plasma flow is also calculated by the LARWM code. Consequently, it is found that the inertial energy of the shear equilibrium plasma flow has an important role in the stabilization of the RWMs.

An Algorithm for Traffic Equilibrium Flow with Capacity Constraints of Arcs

In the traffic equilibrium problem, we introduce capacity constraints of arcs, extend Beckmann’s formula to include these constraints, and give an algorithm for traffic equilibrium flows with capacity constraints on arcs. Using an example, we illustrate the application of the algorithm and show that Beckmann’s formula is a sufficient condition only, not a necessary condition, for traffic equilibrium with capacity constraints of arcs.

Explicit Large Time Stepping with Third-Order Exponential Time Differencing Scheme for Hypersonic Chemical Non-Equilibrium Flow

In this paper, a third-order exponential time differencing scheme, named ETDRK3, was investigated for large time stepping in the computation of hypersonic non-equilibrium flow. The second-order Harten-TVD scheme was used for the spatial discretization. The efficient implementation of the scheme with diagonalization of Jacobin matrix was established and carried out for the semi-cylindrical around flow. Current observations showed that the numerical results were in good agreement with those obtained by the classical explicit three-stage Runge-Kutta scheme (RK3) and implicit LU scheme. Efficiency assessments promised the effectiveness of the ETDRK3 scheme. The rationality of the application of this scheme was proved by its preferable accuracy and efficiency.

基于MoldFlow太阳能储能系统下盖成型模拟及应用

以太阳能储能系统下盖模流分析为例,反复修改流道和浇口截面尺寸与长度以及主流道位置,确定流道尺寸。运用MoldFlow对设计好的流道进行充填分析,以使成型达到流动平衡,并进行冷却、翘曲分析,预测成型缺陷,提出解决措施,为模具设计提供浇注系统和冷却系统方案和注射成型工艺参数,并应用于模具设计和实际生产。

Theoretical investigation of shock stand-off distance for non-equilibrium flows over spheres

We derived a theoretical solution of the shock stand-off distance for a non-equilibrium flow over spheres based on Wen and Hornung＇s solution and Olivier＇s solution. Compared with previous approaches, the main advantage of the present approach is allowing an analytic solution without involving any semi-empirical parameter for the whole non-equilibrium flow regimes. The effects of some important physical quantities therefore can be fully revealed via the analytic solution. By combining the current solution with Ideal Dissociating Gas（IDG） model, we investigate the effects of free stream kinetic energy and free stream dissociation level（which can be very different between different facilities） on the shock stand-off distance.

Numerical Study of Tokamak Equilibrium with Toroidal Flow on EAST

The effect of the toroidal flow on the equilibrium of tokamak plasmas is a sensitive point for high performance plasma and its precise control. In this paper the effect is studied numerically using the EFIT （Equilibrium Fitting） code on EAST （Experimental Advanced Superconducting Tokamak）. Firstly, the numerical calculation exhibits a clear outward shift of pressure contour from the magnetic surfaces in the plasma core and the shift grows with the increase of the toroidal velocity. The peak shift of 8% is observed when the ratio between the plasma velocity and the Alfvdn speed equals to 0.15. Secondly, it is shown that the magnetic surfaces shift outwards from those without flow. With a certain plasma current the safety factor on the magnetic axis decreases as the plasma flow velocity increases. The magnetic shear increases about 10% on the plasma boundary compared with the case without flow.

Three-Dimensional Structure of Non-Equilibrium Homogeneous Condensation Flow in a Supersonic Rectangular Nozzle

Numerical simulations have been carried out for a supersonic three-dimensional rectangular arc nozzle, where a secondary flow toward the center of the curvature occurs due to the shape of the nozzle. It is known that secondary flow causes longitudinal vortices to form near the wall of the nozzle corner, making the nozzle outlet flow unstable and induces loss of transport energy. When the working fluid is a condensable gas with relatively large latent heat such as moist air or steam, rapid accelerated expansion in the nozzle causes non-equilibrium condensation due to supersaturation. After the release of latent heat during phase transition, nozzle flow continues expanding at an equilibrium saturation condition. In the absence of foreign particles, e.g. ions or dust particles, condensation nuclei are formed in the gas itself causing non-equilibrium homogeneous condensation. Supersonic nozzle flow properties vary considerably due to the occurrence of condensation phenomenon. The objective of this study is to investigate the effect of non-equilibrium homogeneous condensation on the longitudinal vortices which form in the range close to the corner of rectangular arc nozzle numerically.

Axisymmetric Toroidal Equilibrium with Sheared Toroidal Flows

Problem of the axisymmetric toroidal equilibrium with pure sheared toroidal flow isinvolved. For standard tokamak equilibrium, general approximate solutions are analytically pur-sued for arbitrary current profile and non-circular cross-section. Equilibrium properties includingthe fiow-induced density asymmetry are analyzed.

On transition of type V interaction in double-wedge flow with non-equilibrium effects

The transition between regular reflection （RR） and Mach reflection （MR） of type V shock-shock interaction on a double-wedge geometry with high temperature non-equilibrium effects is investigated by extended shock-polar method and numerical simulation. First, the critical angles of transition from detachment criterion and yon Neumann criterion are determined by the extended shock-polar method considering the non-equilibrium effects. Then wave patterns and the transition process are numerically obtained. Results of the critical transition angles from shock-polar calculation and numerical simulation show evident disagreement, indicating transition mechanism between RR and MR of type V interaction is changed. By comparing with the frozen counterpart, it is also found that non-equilibrium effects lead to a larger critical wedge angle and a larger hysteresis interval.

泥石流停淤工程应用现状与思考

泥石流综合防治体系主要由稳固、拦挡、排导和停淤工程组成,其中停淤工程发挥重要的减灾作用。在查阅国内外泥石流停淤工程相关资料的基础上,对已建的停淤工程开展野外调查,总结停淤工程在设计和运行过程中存在的问题。具体表现在:1)停淤场内缺乏泥石流分流、导流及均衡停淤措施,导致停淤空间未合理利用;2)停淤工程设计仍以经验设计为主,尤其是停淤量以经验估算为主,计算结果与实际停淤量偏差大;3)停淤场内缺乏快速停淤和减速耗能措施,导致结构受损;4)传统停淤挡墙设计未考虑泥石流冲击力;5)停淤场占地面积与人类使用土地之间的矛盾等。基于以上问题,作者提出泥石流停淤工程均衡停淤的理念,并对以后泥石流停淤工程的设计和研究提出停淤空间优化配置、停淤挡墙结构型式和设计参数优化等方面的思考。

考虑负荷时空均衡和弹性响应的电动汽车快充电价定价策略

为了引导电动汽车有序充电,提出了一种考虑负荷时空均衡和弹性响应的电动汽车快充电价定价策略。引入交通流理论描述交通路网,建立电动汽车快充负荷时空分布模型;考虑配电网调度和电动汽车快充负荷的弹性需求,构建源-荷互动下的快充电价定价架构,并基于潮流追踪法从时空双维度推导快充电价的计算方法;在此基础上,计及电动汽车负荷弹性响应特性,以提升配电网的负荷均衡性为目标,建立快充电价定价策略,并通过迭代算法求解该定价策略。算例仿真结果表明,所提定价策略能够有效引导电动汽车进行有序快充,激励电动汽车用户与配电网友好互动,提升负荷的时空分布均衡性。

R13/R26矩方法的介观尺度壁面边界条件

宏观尺度NSF(Navier-Stokes-Fourier)、R13/R26矩方程边界条件在中、大克努森数Kn来流条件下计算精度大幅度降低,也极易发散。针对这一难题,提出R13/R26矩方程的介观尺度边界条件,在靠近壁面处重构速度分布函数,并输入介观尺度Boltzmann模型方程;基于离散速度法求解宏观参数,所得到的宏观参数作为R13/R26矩方程的壁面边界条件。仿真结果表明:基于介观尺度边界条件的R13/R26矩方法相较原边界条件计算精度最大提高59.84%,同时,所提出的边界条件将矩方法对Kn的适用范围拓展到1.0。

基于水流牵引力的河道岸坡稳定性分析

基于极限平衡理论,结合水平条分法,将Bishop法的竖直条间力关系转换到水平土条上,推导出水流牵引力作用下均质岸坡稳定安全系数的理论计算公式,将其结果与ABAQUS有限元软件的强度折减法模拟的计算结果进行对比分析。结合工程实际,分析水流牵引力对不同坡比河流岸坡的稳定性影响规律。结果表明,理论计算公式与软件模拟的结果基本吻合,误差不超过2.1%。河流中水流牵引力会增大岸坡土体的下滑力矩,降低河流岸坡土体稳定安全系数;当岸坡土体遭受降雨、坡脚土体劣化作用等多因素作用下而处于临界稳定状态时,水流牵引力可能成为滑坡启动的关键因素;在河流岸坡失稳滑动时,水流牵引力将导致滑体向河道方向滑移更远距离,加重滑坡对河流航道安全的危害;坡度越陡,岸坡稳定安全系数受水流牵引力的影响越大。在进行高陡河流岸坡稳定性分析时,水流牵引力是与强降雨、泥石流等因素同样重要且不可忽视的导致岸坡灾变失稳的外部荷载作用。

闪沸喷雾孔几何形状对孔内流动特性影响的数值模拟

研究了汽车直喷汽油机喷嘴的几何形状对于闪沸喷雾孔内流动以及相变过程的影响机理。基于热不平衡假设建立了一维的两相相变流动模型,对于具有不同喷孔流道长度、直径、入口处圆角以及流道锥角的结构,分析了闪沸喷雾孔内流动的特性。将该模型结果与作者团队先前的实验结果进行了精度比对,验证了模型的准确性。结果表明:喷孔流道长度越长,孔径越小,从而孔内相变越剧烈。流道入口处圆角会减少喷孔内部蒸汽的生成。收缩型喷孔压降较小,孔内蒸汽相的生成也相应减少,从而扩张型喷嘴增大蒸汽产生速率。不同的喷孔结构,改变了流道内的压力以及速度分布;压力分布影响了气泡的生长速率,速度分布影响了气泡的生长时间,而两者共同作用影响了孔内的相变特性。

基于宏观基本图的交通控制有效性与路网稳定性研究

区域城市路网在不同控制方法下呈现的网络交通流输出水平与维持能力不尽相同,要评价控制效果的优劣,需要分析区域控制方式下路网交通流与路网耦合时所体现出来的特征值。作为一种路网的基本属性,选择宏观基本图作为研究区域交通控制有效性与路网稳定性的评价载体,解析了相对于路段、交叉口等单点评价具有的优势。基于MFD的区域交通控制评价不受路网交通需求变化的影响。研究建立了路网最大加权流量、最佳累计车辆数、路网负载能力、交通流分布均衡度以及时序均衡度5评价指标,以对区域交通信号控制方法的有效性与路网运行的稳定性进行评价,解读路网高峰时段的交通流维持能力。以成都青羊区太升南路附近37个信号交叉口为路网,利用VISSIM二次开发技术,获得了该路网在定时控制、感应控制、自适应控制以及自适应协调控制下的路网宏观基本图形态。通过对比各控制方法的宏观基本图形态特征与评价指标,从多个维度比较了各控制方法的特征与适用性,分析了相应的控制有效性,解读了其从平峰至过饱和各阶段的交通流维持能力,进而可以了解特定控制方法下路网的运行效率。同时,根据相应控制方法的稳定性表现,指出了各自的局限性,有助于在实际应用中根据区域路网面临的环境,分析应采取的交通控制策略。

浮环弹性变形对浮环动静压轴承润滑特性的影响

浮环轴承在高速工况下运行时,浮环表面在油膜压力作用下会发生弹性变形,影响轴承润滑性能。针对带有深浅腔的浮环动静压轴承,采用有限元法和有限差分法耦合求解油膜Reynolds方程、能量方程和温黏关系式,采用变形矩阵法求解弹性变形方程,计算浮环弹性变形分布;在浮环平衡的基础上,分析浮环变形对环速比、油膜承载力、端泄流量等润滑特性参数的影响。结果表明:浮环弹性变形分布与油膜压力分布呈现一致性,转速越高,偏心越大,变形越明显;考虑浮环弹性变形,浮环达到平衡状态时,内膜偏心率增加,环速比减小,轴承承载力与摩擦力矩均有所增加;由于浮环变形对内、外膜间隙及流动液阻的不同影响,使得内膜端泄流量增加,外膜端泄流量减少。

利用博弈演化算法求解置换Flow shop调度问题

在研究了流程工业中的Flowshop问题的基础上,建立了相应的数学模型,利用基于经济学博弈论的演化博弈算法对经典问题进行了求解,仿真结果证明了算法的有效性。

流场声学层析成像测量方法仿真和实验研究

流速是实现工业生产过程在线监测和精准化控制的重要依据。为准确测得流场分布,提出了基于径向基函数结合均衡优化(RBF-EO)算法的流场声学层析成像方法。采用径向基函数逼近建立声学流场重建模型,利用均衡优化算法求解重建问题中的不适定方程。对典型的四角切圆速度场模型进行了数值模拟与算法的抗噪性检验,并将本算法与传统的重建方法:Tikhonov算法、SVD分解法和灰狼优化算法进行了比较。仿真结果表明该算法能够很好的反演出流场分布,具有较高的重建性能和良好的抗噪性。最后,在实验室进行了1.05 m×1.05 m的测量区域内的流场声学测量实验,并与飘带流场显示和风速仪测量结果进行了对比,结果显示,RBF-EO算法与风速仪测量结果在8个测点的平均误差为9.77%,验证了本文声波流场测量方法的可靠性。

旋流场中夹杂物运动行为的数值模拟

在冶金过程中,离心中间包、旋流水口通过旋转钢液使夹杂物聚集,进而去除钢液中夹杂物.为研究夹杂物在旋流场中的聚集机理,建立了基于Eulerian-Lagrangian法的颗粒运动模型,对旋流场中单个夹杂物颗粒的运动行为进行数值模拟.结果表明:在各力及惯性的作用下,旋流场中夹杂物的运动存在稳定的平衡轨道;夹杂物粒径为50,100μm时,其Stokes数远小于1,夹杂物紧随钢液运动;夹杂物粒径为200,500μm时,粒径越大,平衡轨道半径r_(e)越小;当夹杂物与钢液的密度比ρp/ρ由0.63分别降至0.55,0.47,0.38时,r_(e)分别相对减小46.5%,33.3%,2.23%;在旋流转速为5.24~11.51 rad/s的条件下,旋流转速每提高2.09 rad/s,r_(e)分别相对减小1.30%,2.35%,27.2%.

Geodesic acoustic modes in tokamak plasmas with anisotropic distribution and a radial equilibrium electric field

The dispersion relation of standard geodesic acoustic modes in tokamak plasmas with anisotropic distribution and a radial equilibrium electric field is derived and analyzed. Both frequencies and damping rates increase with respect to the poloidal Mach number which indicates the strength of the radial electric field. The strength of anisotropy is denoted by the ratio of the parallel temperature（T_‖） to the perpendicular temperature（T_⊥）. It is shown that, when the parallel temperature is lower than the perpendicular temperature, the enhanced anisotropy tends to enlarge the real frequency but reduces the damping rate, and when the parallel temperature is higher than the perpendicular temperature, the effect is opposite. The radial equilibrium electric field has stronger effect on the frequency and damping rate for the case with higher parallel temperature than the case with higher perpendicular temperature.