涡重联过程中背景涡量增长的机制研究

采用拟谱方法求解N-S方程,直接模拟了两个反向平行涡管的重联过程,考察了各种扰动方式对涡重联的影响,发现了"弧形涡带"现象,着重分析了背景涡量增长的物理机制。     

椭球坐标系的航迹模拟

建立了基于椭球坐标系下的目标运动模型,并根据实际情况进行加噪和坐标转换,对飞行目标的航迹进行了模拟。实例表明,该模型设计正确、合理,能充分的考虑到球形坐标的特性,与实际飞行情况比较吻合。     

用于导航定位坐标系转换的引申迭代算法研究

为了提升卫星导航信号处理软件RTKLIB的直角坐标转换至大地坐标算法的性能,本文基于牛顿迭代算法的思路,在Bowring直接解法基础上提出一种引申迭代算法。经过理论分析和测试实验数据对比,本文证实了引申迭代坐标转换算法相对于RTILIB现有的一般迭代坐标转换算法,具有迭代次数更少、精度更高的特点,更适用于高度坐标h取值较大的情形。     

贴体坐标系下模型加力室的大涡模拟

本文利用贴体网格对带V形槽稳定器模型加力燃烧室素流化学反应流流动进行大涡模拟的研究。采用区域法生成模型加力燃烧室的二维贴体网格,并采用多区域耦合法进行区域之间的数据传递,求解加力室整体流场。采用k方程亚网格尺度模型和亚网格EBU燃烧模型分别估算其亚网格紊流粘性和化学反应速率,用热通量辐射模型估算辐射通量,并用交错网格下SIMPLE算法和混合差分格式求解离散方程,壁面函数处理固壁边界条件。计算结果显示了稳定器后面的回流区气流结构,所得的热态流场模拟结果与实验比较吻合,表明采用贴体网格对模型加力燃烧室进行大涡模拟能真实反映流体流动及燃烧过程。     

非晶铁中位形熵与信息维的压力响应

本文分析了非晶铁模型中原子能量分布的信息维和位形熵随压力的变化。计算了原子相互作用能的粒子数分布,将其分布的信息维作为非晶态位形熵的度量。计算结果表明,原子能量分布曲线和位形熵与统计时所取能量间隔有关;位形熵与能量间隔之间具有分形标度关系。用介于由能量间隔的下截止限和上截止限所确定的无标度区内的平均值表示各压力下的位形熵。模拟结果表明,原子能量分布的信息维是描述非晶系统无序状态的另一有效参量;压力对非晶金属结构无序及分维值的影响呈较复杂的波动变化趋势。 关键词：     

不同磁致纵向涡形式对空气对流换热的影响

为揭示不同磁致纵向涡对通道内空气对流换热的影响规律,分别就两极和四极钕铁硼永磁体作用下的矩形通道内的对流换热进行了数值模拟。模拟以通道入口段的流动和换热为对象,得到了不同Re和不同壁温下的流场和温度场, 对流换热的Nu和阻力系数,以及场协同数Fc。结果表明,不同纵向涡形式下的流场和温度场的协同性不同,具有八纵向涡形式的对流换热的协同性优于四纵向涡形式,强化效果也优于四纵向涡。     

扁管管片式散热器中马蹄形涡的数值模拟

本文通过数值模拟的方法对扁管管片式散热器中的流场、涡量场、速度环量、 Nu数、马蹄形涡进行了模拟。在Re=1450时,对马蹄形涡的形成、发展、衰减进行了模拟。对在Re=1050时平均Nu数在流动方向的分布,与横断面上速度环量在流动方向的分布进行了比较分析,得出在扁管管片式散热器中决定换热能力的物理量-速度环量。     

对相干态在通过参量转换中的演化与量子化光涡态的实现

本文讨论了光学参量频率转换过程中对相干态的演化问题, 获得了对相干态时间演化的解析表达式及在位形空间的波函数, 发现通过适当调节系统元件及相互作用时间, 对相干态在位形空间中的波包能呈现出量子涡态特性, 并且与这样涡态相关的波函数具有修正Bessel-Gaussian形式的结构, 即非高斯型波函数. 在相干态表象下, 这一量子化涡态是两模湮没算符平方和的本征态. 这一讨论揭示了产生量子化涡态的另一可实现方案.     

来流边界层对三角翼诱导涡特性的影响

三角翼是涡发生器的主要结构型式,用于涡发生器的三角翼常处于翼面边界层内。本文采用数值求解雷诺平均NS方程的方法,以平板上一个三角翼模型为研究对象,研究不同来流边界层速度型(均匀分布、湍流边界层速度型和层流边界层速度型)和5种边界层厚度条件下,三角翼诱导涡沿流向的最大涡量分布规律及衰减规律。结果表明,湍流边界层下三角翼诱导涡最大涡量值要大于层流边界层,且边界层高度越低,诱导涡最大涡量值越大。     

小翼对风力机叶尖涡运动轨迹的影响研究

本文利用三维PIV测速技术,在B1/K2直流式低速风洞开口段,对小翼对风力机叶尖涡三维运动轨迹的影响展开研究。实验发现,S型小翼对叶尖涡的打散程度大于V型小翼。加装小翼后,使得叶尖涡运动轨迹螺距减小,同时叶尖涡的径向运动距离增加,向外迁移的程度增加。在额定工况下,小翼影响的因素包括风力机功率系数、叶尖涡运动轨迹形态、叶尖涡的强弱,其中小翼对叶尖涡运动轨迹向外迁移的程度和螺距的减小程度占主导因素,小翼对叶尖涡打散程度占次要因素。     

椭圆柱坐标下等值坐标带电导体柱的电势与电场分布

利用椭圆柱坐标求解共焦共轴带电导体双椭圆柱和双曲柱电势和电场的分布,并对一些特例作了讨论.     

The time fractional heat conduction equation in the general orthogonal curvilinear coordinate and the cylindrical coordinate systems

In this paper a time fractional Fourier law is obtained from fractional calculus. According to the fractional Fourier law, a fractional heat conduction equation with a time fractional derivative in the general orthogonal curvilinear coordinate system is built. The fractional heat conduction equations in other orthogonal coordinate systems are readily obtainable as special cases. In addition, we obtain the solution of the fractional heat conduction equation in the cylindrical coordinate system in terms of the generalized H-function using integral transformation methods. The fractional heat conduction equation in the case 0<α≤1 interpolates the standard heat conduction equation (α=1) and the Localized heat conduction equation (α→0). Finally, numerical results are presented graphically for various values of order of fractional derivative.     

多自由度线性微幅振动系统简正坐标的一般求法

给出了动能矩阵为对角矩阵,在A=aE和A≠aE(E为单位矩阵)两种情况下同时对角化势能矩阵求简正坐标的一般方法,并提出了先改变坐标标度,后对角化新势能矩阵或用频率特征矩阵的伴随矩阵的任一列求简正坐标的另两种方法．     

Symmetry analysis and explicit solutions of the (3+1)-dimensional baroclinic potential vorticity equation

<正>This paper investigates an important high-dimensional model in the atmospheric and oceanic dynamics-(3+l)- dimensional nonlinear baroclinic potential vorticity equation by the classical Lie group method.Its symmetry algebra, symmetry group and group-invariant solutions are analysed.Otherwise,some exact explicit solutions are obtained from the corresponding(2+1)-dimensional equation,the inviscid barotropic nondivergent vorticy equation.To show the properties and characters of these solutions,some plots as well as their possible physical meanings of the atmospheric circulation are given.     

平流涡度方程及其在2006年Bilis台风分析中的应用

推导得到气压坐标中的动量叉乘形式的垂直涡度方程,这个动量叉乘形式的涡度方程包含了水平风的平流旋转效应,可称为平流涡度方程.由于水平风场的平流作用可由等压面天气图直观分析得到,因此平流涡度方程可方便用于实际天气分析.对2006年的Bilis台风移动过程中由经典涡度方程和平流涡度方程计算得到的垂直涡度倾向进行对比分析发现,二者计算得到的垂直涡度倾向变化的分布形式接近,但平流涡度方程计算得到的倾向的数值明显大于经典涡度方程的数值,正负涡度倾向区也更集中.对Bilis移动过程中的垂直涡度方程和平流涡度方程中各项的计算分析表明,水平风场的平流旋转作用是Bilis发展移动过程中垂直涡度变化的一个主要因素,是造成垂直涡度增强并发展的主要原因.因此,当水平风场平流旋转效应较强时,平流作用对垂直涡度倾向变化起主导作用,可直接用平流项来近似分析Bilis台风的涡度变化.而平流涡度方程中地转涡度和散度项的变化趋势与Bilis台风的移动路径有较好的一致性,这一项对台风的移动路径预报有更好的指示意义.     

在点正则变换下双原子分子的广义Hulthén势映射至P(o)schl-Teller Ⅰ势

利用在点正则变换下形状不变势的映射方法,找出了该问题需要的点正则变换,建立了双原子分子的广义Hulthén势和Pschl-Teller Ⅰ势之间的关系,并由Pschl-Teller Ⅰ势的束缚态能级和波函数,方便地求得了广义Hulthén势的束缚态能级和波函数.     

用双极坐标求解带电导体圆柱和无限大接地导体平板间的电势

利用双极坐标求解了带电导体圆柱和无限大接地导体平板间的电势分布,并对带电导体圆柱表面的电荷分布及无限大接地导体平板表面的电荷分布作了讨论.     

An efficientmethod to determine chemical potential of mixtures in the isothermal and isobaric bulk phase with kineticMonte Carlo simulation

A kinetic Monte Carlo (kMC) scheme in the NPT ensemble (constant number of molecules, pressure and temperature) has been developed to determine accurate chemical potentials for all components in a homogeneous mixture. The simulation requires two moves: (1) a displacement move and (2) a volume change move. In the former, the mobility rate of a selected molecule is determined by its interaction with all the other molecules in the system and is moved to a random position within the simulation box, according to the Rosenbluth algorithm, without any rejections (entropic sampling). The volume change move is decided by a comparison between either the instant pressure or the partial average pressure (with long-range correction) and the specified pressure and is carried out much less frequently than the displacement move. We applied this NPT scheme to a number of mixtures in both the gaseous and liquid phases, and show that the derived chemical potentials are accurate and reproducible. The method is recommended for obtaining chemical potentials in mixtures that are required as input in a grand canonical ensemble simulation.     

新乌龟坐标变换下的动态Kinnersley黑洞的Hawking辐射

采用两种新的乌龟坐标变换,用改进的Damour-Ruffini方法研究了动态Kinnersley黑洞的Hawking辐射.在新乌龟坐标变换下,将Klein-Gordon方程在视界附近变换成平直时空的标准波动方程形式,得到了黑洞的表面引力及Hawking温度,该温度在黑洞表面不同点有不同的值.值得注意的是,旧的乌龟坐标变换存在量纲错误,新乌龟坐标变换没有量纲问题,选不同的旧乌龟坐标变换计算同一黑洞所得结果不同,但是采用不同的新乌龟坐标变换所得结果仍然不同. 关键词： 黑洞 乌龟坐标变换 Hawking辐射 Klein-Gorden方程     

Geometrical statistics of the vorticity vector and the strain rate tensor in rotating turbulence

We report results on the geometrical statistics of the vorticity vector obtained from experiments in electromagnetically forced rotating turbulence. A range of rotation rates Ω is considered, from non-rotating to rapidly rotating turbulence with a maximum background rotation rate of Ω = 5 rad/s (with Rossby number much smaller than unity). Typically, the Taylor-scale Reynolds number in our experiments is around Re_λ ≈ 100. The measurement volume is located in the centre of the fluid container above the bottom boundary layer, where the turbulent flow can be considered locally statistically isotropic and horizontally homogeneous for the non-rotating case, see L.J.A. van Bokhoven, H.J.H. Clercx, G.J.F. van Heijst, and R.R. Trieling, Experiments on rapidly rotating turbulent flows, Phys. Fluids 21 (2009) 096601. Based on the full set of velocity derivatives, measured in a Lagrangian way by three-dimensional (3D) particle tracking velocimetry, we have been able to quantify statistically the effect of system rotation on several flow properties. For the range of rotation rates considered, the experimental results show how the turbulence evolves from almost isotropic 3D turbulence (Ω ? 0.2 rad/s) to quasi-two-dimensional turbulence (Ω ≈ 5.0 rad/s), and how this is reflected by several statistical quantities. In particular, we have studied the orientation of the vorticity vector with respect to the three eigenvectors of the local strain rate tensor and with respect to the vortex stretching vector. Additionally, we have quantified the role of system rotation on the self-amplification terms of the enstrophy and strain rate equations and the direct contribution of the background rotation on these evolution equations. The main effect of background rotation is the strong reduction of extreme events and related (strong) reduction of the skewness of PDFs of several quantities, for example, the intermediate eigenvalue of the strain rate tensor and the enstrophy self-amplification term.