基于流体动力学模型的2维砷化镓金属半导体场效应管数值模拟

 介绍了用于描述工作在高频强电场条件下的亚微米半导体器件的流体动力学模型,并讨论了为求解流体动力学模型所采用的算子分裂方法和有限体积法。使用流体动力学模型,对亚微米GaAs金属半导体场效应管器件进行了2维数值模拟,得到了该器件的I-V曲线、电子密度分布和电子温度分布。数值模拟结果表明,器件栅极电压越负,肖特基结的耗尽层越厚,源漏电流越小;在耗尽层内电场最强处,电子温度达到4 000 K;在强电场下,电子温度将严重偏离晶格温度,形成所谓热电子。     

微重力池沸腾现象中的临界热流密度

本文利用我国第22颗返回式卫星实验研究了微重力条件下池沸腾临界热流现象,发现基于流体动力学不稳定性机制的LD-Zuber模型可以很好地预测不同重力条件下的池沸腾临界热流变化趋势,尽管热丝无量纲半径比该模型的适用范围扩大了3～4个数量级.这和地面常重力环境中关于临界热流尺度效应的研究结果有很大差异,表明在Bond数很小时,热丝无量纲半径已不再是描述临界热流尺度效应的唯一参数.此外,本文提出了"极限核化尺寸"的概念,来解释了不同条件下临界热流的变化特征.     

垂直振动颗粒混合气体的振荡现象研究

运用事件驱动算法研究颗粒混合物在垂直振动容器中的振荡现象.容器被具有一定高度的隔板分成相等大小的两个小室,并采用半径相差一倍的两种颗粒.研究结果表明,颗粒振荡周期随两种颗粒密度比的减少而急剧增加.通过计算在垂直方向上两种颗粒高度之比随颗粒密度的变化关系,说明决定颗粒振荡与否的主要因素并不是"巴西坚果效应"或"反巴西坚果效应".通过计算颗粒温度,发现颗粒振荡取决于颗粒混合气体的小颗粒温度.当小颗粒温度大于一定值时,颗粒混合气体发生颗粒振荡现象.根据Viridi等提出的流体动力学模型,文中对该模型做出相应的修改,加入密度因子,从而可以解释颗粒振荡周期与颗粒密度比的关系.     

爆炸焊接斜碰撞过程的数值模拟

 借助动力学分析软件ANSYS/LS-DYNA 11.0,建立了考虑材料强度的流体弹塑性力学模型,运用光滑粒子流体动力学（SPH）方法,对爆炸焊接斜碰撞过程进行了数值模拟。界面波和射流的模拟结果与爆炸焊接生产实际中的现象较为吻合,说明采用SPH方法对爆炸焊接斜碰撞过程进行模拟研究是有科学价值的。     

超临界压力RP-3起始加热段传热恶化数值研究

使用开源流体动力学程序库OpenFOAM对竖直圆管内超临界压力RP-3对流传热进行数值模拟,研究重点为起始加热段的传热恶化现象。本文选择k-ε-v~2-f和k-ωSST两种低Re数湍流模型进行计算并与实验数据进行对比,讨论了两种模型对于高壁面热流条件下传热恶化现象的预测能力.通过对流场及温度场的分析对起始加热段传热恶化现象给出机理解释,最后考察了变物性及浮升力的影响。结果表明:k-ωSST模型无法模拟传热恶化;k-ε-v~2-f模型能够定性描述起始加热段内壁温的迅速升高。由流体密度变化及重力引起的浮升力作用是导致起始加热段传热恶化的重要原因。     

基于自相似模型的二维X射线激光等离子体流体力学

从自相似方法出发,建立了简化的二维X射线激光等离子体流体动力学模型. 利用该模型研究了平板靶X射线激光的二维流体力学行为. 研究表明,当激光作用结束后,经过一段时间的演化电子密度和温度沿线聚焦方向逐渐达到平衡,该结果对X射线激光的优化设计具有重要意义. 关键词： X射线激光 二维流体力学计算 自相似方法     

含Laplace-Gauss型混合噪声图像二阶正则化重建方法

假设观测数据含Laplace-Gauss型混合噪声条件下,提出求解数据重建反问题的一种新型一阶二阶混合正则化模型,阐述该模型在断层重建和流体动力学实验定量诊断中的应用.建模过程采用贝叶斯推断理论和期望极大方法,将空间自适应函数引入经典的增广拉格朗日方法得到模型数值算法.所提出的模型及其算法进行图像复原和客体重建实验.结果表明模型算法的可靠性.     

含Laplace-Gauss型混合噪声图像二阶正则化重建方法（英文）

假设观测数据含Laplace-Gauss型混合噪声条件下,提出求解数据重建反问题的一种新型一阶二阶混合正则化模型,阐述该模型在断层重建和流体动力学实验定量诊断中的应用.建模过程采用贝叶斯推断理论和期望极大方法,将空间自适应函数引入经典的增广拉格朗日方法得到模型数值算法.所提出的模型及其算法进行图像复原和客体重建实验.结果表明模型算法的可靠性.     

金属表面几何缺陷微细结构对微喷射特性的影响

基于光滑粒子流体动力学方法, 分别采用实测样品几何缺陷模型和简化V形沟槽模型对铅的微喷射过程进行了模拟. 重点分析了金属表面几何缺陷微细结构对微喷射特性的影响, 并将数值计算结果与相应的实验测量值进行对比. 结果表明, 基于实测样品几何缺陷模型计算的最快喷射速度和累积喷射量与实验测量结果符合得很好. 进一步研究发现, 在实测样品几何缺陷诱导的微喷射过程中存在“二次汇聚喷射”现象, 与单次喷射相比, 该过程会诱导产生更高的喷射速度并显著影响微喷物的空间密度分布. 这说明除了受扰动波长、深度影响外,表面几何缺陷微细结构也是影响金属微喷射过程的重要因素.     

一个新的用于不可压磁流体动力学的格子波尔兹曼模型

绝大多数现有的格子波尔兹曼磁流体动力学模型其实是用可压缩方法来模拟不可压磁流体。而这些可压缩效应在数值模拟中往往会带来意想不到的误差。在这篇文章中，我们提出了一个全新的可用于的不可压格子波尔兹曼磁流体动力学模型，并且进行了哈特曼流的数值模拟。模拟结果与哈特曼流的解析解非常吻合。这个方法需要一个假设条件来消除误差。我们做了大量的数值试验，并且与Dellar教授的模型进行了详细的分析与比较。     

Flow waves of hierarchical pattern formation induced by chemical waves: The birth, growth and death of hydrodynamic structures

We introduce a short review of chemically driven convection together with a series of our experiments on hydrodynamic instabilities induced by chemical waves excited in the batch reactor of a Belousov-Zhabotinsky reaction. Several unresolved phenomena are picked out and possible mechanisms are discussed extensively. Interesting features of these phenomena can be summarized as being caused by the ‘global and dynamic hydrodynamic pattern induced by chemical waves’. These chemically induced global pattern of hydrodynamic phenomena may not be simply explained by the reaction-diffusion-convection model based on Marangoni instability (surface tension-driven convection), which produces only a localized structure of the convection pattern. Observed flow waves show global and dynamic patterns of convection that generate a functional structure associated with hierarchical patterns appearing in the reaction-diffusion-convection system. In particular, we clarify the existence of a continuous stream of hydrodynamic flow with growing amplitude and its rotating direction. We find that the flow does not stabilize to a motionless state until the system has self-collapsed. This new picture of the flow waves requires a revision of the reaction-diffusion-convection model. The established flow structure can be regarded as a mixing and/or transport process to supply the substrate from the peripheral region to the centre of the chemical waves to sustain the reaction. This characteristic may be a function of the hierarchical structure. A new mechanism for the viscous-elastic feature of the gas-liquid interface is discussed in order to understand these curious phenomena of interest.     

Determination of the quench velocity and rewetting temperature of hot surfaces: Formulation of a nonisothermal microscale hydrodynamic model

A nonisothermal microscale model of the three-phase, solid-liquid-gas, contact zone is formulated in the context of rewetting phenomena. The model incorporates hydrodynamics, heat transfer, interfacial phenomena, and intermolecular long range forces, in a two-dimensional proximal region of the order of 1000 A in width and 100 A in thickness. The model comprises scaled mass, momentum, and energy balances, and their corresponding scaled boundary conditions. The small contact angles which are characteristic of rewetting situations facilitate the use of the lubrication approximation, and the dynamics of the liquid and gas phases is decoupled by applying the one-sided simplification. The microscale hydrodynamic model reflects the strong effect of the solid-liquid interactions on the film profile, and the attendant flow and thermal fields. Thinner films having smaller contact angles involve stronger solid-liquid attraction forces, and consequently they exhibit higher rewetting temperatures and lower evaporation and vapor recoil effects. Thermocapillary and evaporation and conduction effects are expressed by appropriate dimensionless numbers. A set of such numbers is defined in the context of the differential equations of the microscale model. This model covers the hydrodynamic aspect of rewetting phenomena, which are also controlled by thermodynamic and macroscale constraints. This calls for interfacing and appropriate combination between the microscale hydrodynamic model, thermodynamics, and other macroscale rewetting models, for the determination of rewetting temperatures and quench velocities of liquids on hot solid surfaces. This is addressed elsewhere, in subsequent papers that follow this work.     

激光表面纹理化过程中的Rayleight-Taylor不稳定性

 用表面纹理化的热模型,分析了固体表面的熔化和重固化的物理过程,计算了在纹理化过程中的表面温度,穿透深度,熔化深度,相面移动速度等物理量,提出了Rayleight-Taylor不稳定性形成周期化结构的机理。     

Discrete Boltzmann model for implosion- and explosion-related compressible flow with spherical symmetry

To kinetically model implosion- and explosion-related phenomena, we present a theoretical framework for constructing a discrete Boltzmann model (DBM) with spherical symmetry in spherical coordinates. To achieve this goal, a key technique is to use localCartesian coordinates to describe the particle velocity in the kinetic model. Therefore, geometric effects, such as divergence and convergence, are described as a “force term”. To better access the nonequilibrium behavior, even though the corresponding hydrodynamic model is one-dimensional, the DBM uses a discrete velocity model (DVM) with three dimensions. A new scheme is introduced so that the DBM can use the same DVM regardless of whether or not there are extra degrees of freedom. As an example, a DVM with 26 velocities is formulated to construct the DBM at the Navier–Stokes level. Via the DBM, one can study simultaneously the hydrodynamic and thermodynamic nonequilibrium behaviors in implosion and explosion processes that are not very close to the spherical center. The extension of the current model to a multiple-relaxation-time version is straightforward.     

一个完全守恒的格子Boltzmann模型

利用六角形格子离散的方法,使得每个六角形Cell里含有 3种不同运动速度的粒子微团,宏观物理量用这些粒子微团的矩来定义.根据微观和宏观之间的质量、动量、能量守恒准则,建立了一个二维的D2Q19格子Boltzmann模型,从该D2Q19模型出发可推导出宏观的流体力学方程组.用该模型对冲击波在障碍物组表面上的折射现象进行数值模拟,并将计算结果与实验进行了比较.     

Nonlinear finite amplitude vibrations of sharp-edged beams in viscous fluids

In this paper, we study flexural vibrations of a cantilever beam with thin rectangular cross section submerged in a quiescent viscous fluid and undergoing oscillations whose amplitude is comparable with its width. The structure is modeled using Euler–Bernoulli beam theory and the distributed hydrodynamic loading is described by a single complex-valued hydrodynamic function which accounts for added mass and fluid damping experienced by the structure. We perform a parametric 2D computational fluid dynamics analysis of an oscillating rigid lamina, representative of a generic beam cross section, to understand the dependence of the hydrodynamic function on the governing flow parameters. We find that increasing the frequency and amplitude of the vibration elicits vortex shedding and convection phenomena which are, in turn, responsible for nonlinear hydrodynamic damping. We establish a manageable nonlinear correction to the classical hydrodynamic function developed for small amplitude vibration and we derive a computationally efficient reduced order modal model for the beam nonlinear oscillations. Numerical and theoretical results are validated by comparison with ad hoc designed experiments on tapered beams and multimodal vibrations and with data available in the literature. Findings from this work are expected to find applications in the design of slender structures of interest in marine applications, such as biomimetic propulsion systems and energy harvesting devices.     

Time-dependent Ginzburg-Landau equation for lattice hydrodynamic model describing pedestrian flow

A thermodynamic theory is formulated to describe the phase transition and critical phenomena in pedestrian flow. Based on the extended lattice hydrodynamic pedestrian model taking the interaction of the next-nearest-neighbor persons into account, the time-dependent Ginzburg-Landau (TDGL) equation is derived to describe the pedestrian flow near the critical point through the nonlinear analysis method. The corresponding two solutions, the uniform and the kink solutions, are given. The coexisting curve, spinodal line, and critical point are obtained by the first and second derivatives of the thermodynamic potential.     

An Exact Semi-Inverse Solution for the Family of Geophysical Problems of a Draining Slope

Doklady Physics - One of the main causes of the appearance of dangerous geophysical slope phenomena is water saturation of slopes and the negative hydrodynamic impact of a stream of underground...