Brown凝并中两个不同直径纳米颗粒的碰撞系数

对Brown凝并中两个不同直径纳米颗粒的碰撞系数进行了研究,通过求解碰撞方程,获得了在van der Waals力和弹性变形力作用下,直径为100 nm至750 nm的邻苯二甲酸二辛酯纳米颗粒的碰撞系数．发现碰撞系数总体上随着颗粒直径和2个颗粒半径比的增加而减小;当颗粒直径为550 nm时,碰撞系数有一个突然的增加．最后给出了具有不同直径2个纳米颗粒碰撞系数的新表达式．     

气固两相流和气液两相流的掺混问题

在工业生产中气固两相流和气液两相流的掺混是一个常见问题.在这个掺混流动过程中,颗粒团将形成,且在颗粒碰撞聚结效应和分裂效应相平衡时,颗粒团将具有稳定半径.本文引入了颗粒团线尺度数密度分布函数n(a,,t),从分子运动论的观点出发,导出了颗粒团线尺度数密度分布函数的控制方程.最后,在气相流速非常缓慢的情况下,得到了颗粒团平均稳定半径的表达式.     

室内细颗粒物碰撞模型及碰撞结果讨论

为了研究室内细颗粒物凝并机理,基于统计平均及颗粒物随机运动的思想对室内细颗粒物碰壁数和细颗粒物之间发生对心碰撞的概率进行了总结计算,并对碰撞之后的结果进行了定量和定性的分析,得到了0.3μm的DOP颗粒的最终压缩变形与碰撞发生初始速度以及碰撞效率随粒径变化曲线.颗粒物碰撞后凝并的可能性会随着颗粒碰撞初速度的增加而降低,小粒径颗粒发生碰撞后凝并的可能性一般会大于大粒径颗粒,碰撞效率随粒径的增大而减小.     

平面射流中纳米粒子积聚的矩方法

应用大涡模拟方法求解平面湍射流场,矩方法求解纳米粒子的一般动力学方程．通过对每种情况3 000个时间步的平均,得到了Schmidt数和Damkohler数对纳米粒子动力学特性的影响．结果发现, 当气体参数不变时,Schmidt数的变化只对直径小于1 nm的颗粒数密度的分布产生影响．直径小的颗粒其颗粒数密度沿流动方向下降迅速,而具有大Schmidt数的颗粒,沿横向的分布较窄．较小的颗粒容易发生积聚和扩散,并且体积增长较快,因而颗粒多分散性较为明显．小的颗粒积聚时间尺度能增强颗粒的碰撞和积聚频率,导致颗粒尺寸迅速增大．Damkohler数越大,颗粒的多分散也越明显．     

螺旋型旋风分离器两相流场的数值模拟

对螺旋型旋风分离器进行了两相流场的三维数值模拟．气体流场通过求解三维N-S方程得到,湍流模型采用了雷诺应力模型．计算结果表明,旋风分离器内部的流场分为两部分:螺旋通道内比较稳定的流场和筒体中心区域的复合涡结构流场．对颗粒运动轨迹的计算表明,颗粒在入口处的初始位置对颗粒分离有比较显著的影响．同时得到了不同入口速度下颗粒的分级效率曲线,并给出了气体流量对旋风分离器性能的影响,结果显示:气体流量的增加会提高分离效率,但同时导致压力损失的急剧增加．     

泥石流固液分相流速计算方法研究

泥石流固液分相流速是泥石流对岸坡、防治结构冲击、磨损机理的核心问题．将泥石流体简化为具有相同粒径的固相和具有相同力学性质的液相,基于泥石流体为沿流动方向的一维两相流体,运用两相流理论建立了泥石流固液分相流速控制方程．构建了泥石流平均压力、彻体力及平均表面力的计算方法,尤其通过浆体的Binhanm体流变方程、Bagnold颗粒相互作用试验成果建立了控制体平均表面力计算方法;建立了固液两相流速比例系数,以及理论固相流速与实际流速的比例系数．据此求解控制方程得到了固液分相流速计算方法,该方法既可同时适用于粘性泥石流和稀性泥石流,也可在泥石流爆发以后通过现场采集沉积物分析反求泥石流爆发期间的分相流速．工程实例分析显示,该方法计算结果与实测结果吻合较好．     

自然弯扭梁广义翘曲坐标的求解

提出了自然弯扭梁受复杂载荷作用时静力分析的一种理论方法,重点在于对控制方程的求解,其中考虑了与扭转有关的翘曲变形和横向剪切变形的影响．在特殊的情况下,可以比较容易地得到这些方程的解答,包括各种内力、应力、应变和位移的计算．算例给出了平面曲梁受水平和垂直分布载荷作用时广义翘曲坐标的求解方法．计算结果表明,求得的应力和位移的理论值和三维有限元结果非常接近．此外,该理论不限于具有双对称横截面的自然弯扭梁,同样可推广至具有一般横截面形状的情况．     

再论二相流基本方程——关于固相碰撞应力的讨论

论述了:( 1 )相界面上有两种彼此独立的相互作用 :相间相互作用和碰撞相互作用 ,相界面上的间断关系可作相应的分解 ;( 2 )颗粒中的应力可分解为本底应力和碰撞应力 ,它们分别对应于相界面上的相间作用和碰撞作用 ;( 3)通过相界面 ,碰撞应力没有间断 ,因此 ,对于它 ,导数的平均值等于平均值的导数 ;( 4)基本方程中的固相应力应包含碰撞应力 ,而相间力表达式中的固相应力只含本底应力 .通过这些论述 ,将Drew和Ishii等发展起来的一种相当严谨的推导二相流基本方程的方法 ,推广到浓密的二相流 ,得到了包括碰撞应力效应的二相流平均运动方程组.     

三角形弹性夹杂对裂纹的影响

研究了三角形弹性夹杂和裂纹之间的相互影响问题。应用Chau和Wang导出的面力边值问题的边界积分方程为基本方程,用夹杂和基体交界面上的面力和位移的连续性条件为补充方程,从而得到了一组能够解决夹杂和裂纹相互影响问题的方程,最后的方程组用一种新的边界单元法求解。计算了各种不同的夹杂和基体的材料常数以及夹杂和基体之间不同距离情况下裂纹尖端的应力强度因子。文中结果对研究新型复合材料有一定的应用价值。     

悬移质与推移质分层管流的阻力特性

本文着重探讨管道中悬移质与推移质分层流动的阻力特性.文中提出,粗颗粒、高浓度的两相流动中,颗粒间的碰撞力对颗粒的悬浮和运动起着重要的作用.在这个理论基础上,导出了阻力系数公式,并得到验证.试验证明,扩散理论不足以描述这类流动.粗颗粒的悬浮运动是否增耗水流的能量,主要取决于碰撞力与紊动力之间的对比消长.在高浓度情况下,粗颗粒悬移质明显地增大了水流的能量损失.推移质的存在将使两相流动的阻力损失显著增大,其增阻率与水流条件及颗粒特性之间存在有一定的函数关系.     

Hydrodynamic Models with Quantum Corrections

We derive a quantum-corrected hydrodynamic and drift-diffusion model for the out-of-equilibrium particle dynamics in the presence of particle collisions, modeled by a BGK collision term. The quantum mechanical corrections are obtained within the Liouville formalism and are expressed by an effective nonlinear force. The Boltzmann and Fermi-Dirac statistics are included.     

An improvement of chaos-based hash function in cryptanalysis approach: An experience with chaotic neural networks and semi-collision attack

In this paper, the chaos-based hash function is analyzed, then an improved version of chaos-based hash function is presented and discussed using chaotic neural networks. It is based on the piecewise linear chaotic map that is used as a transfer function in the input and output of the neural network layer. The security of the improved hash function is also discussed and a novel type of collision resistant hash function called semi-collision attack is proposed, which is based on the collision percentage between the two hash values. In the proposed attack particle swarm optimization algorithm is used to define the fitness function parameters. Finally, numerical and simulation results provides strong collision resistance and high performance efficiency.     

Effect of spherically symmetric mass flow from the surface of a particle on the force of interaction with a plane surface

A stationary velocity field of the flow of a gaseous medium generated by uniform radial injection from the surface of a spherical particle near a wall is considered in the Stokes' approximation. Bispherical coordinates are used to write the expression for the stream function. A formula is obtained for the force acting on the spherical particle when there is an arbitrary mass flow from its surface, generalizing earlier results /1, 2/. An expression for the force acting on the particle is obtained for the case of spherically symmetric injection from the surface of the particle, and asymptotic formulas at short and long distances from the wall are studied.

An analogous problem concerning the forces of interaction between two spherical particles of the same radius, when uniform injection of equal intensity takes place from their surfaces, is discussed. This is equivalent to the problem of the interaction of a spherical particle with a free surface. A general expression for the force of interaction, and its asymptotic forms for short and long distances, are obtained.     

双尺度二阶矩颗粒相湍流模型经验系数的影响

基于将颗粒脉动分成湍流引起的大尺度脉动和颗粒间碰撞产生的小尺度脉动的概念,建立了双尺度二阶矩两相湍流模型．用该模型对下行床内两相流动进行了数值模拟,颗粒体积浓度、平均速度的计算结果和实验数据吻合较好．分析了双尺度二阶矩两相湍流模型经验系数变化对预报结果的影响:在经验系数的一定变化范围内,预报结果并无明显的影响,但是变化范围增大,预报结果会产生较大变化．     

A further discussion on basic equations for two-phase flow

The following points are argued: (i) there are two independent kinds of interaction on interfaces, i.e. the interaction between phases and the collision interaction, and the jump relations on interfaces can accordingly be resolved; (ii) the stress in a particle can also be divided into background stress and collision stress corresponding to the two kinds of interaction on interfaces respectively; (iii) the collision stress, in fact, has no jump on interface, so the averaged value of its derivative is equal to the derivative of its averaged value; (iv) the stress of solid phase in the basic equations for two-phase flow should include the collision stress, while the stress in the expression of the inter-phase force contains the background one only. Based on the arguments, the strict method for deriving the equations for two-phase flow developed by Drew, Ishii et al. is generalized to the dense two-phase flow, which involves the effect of collision stress.     

Sinai Billiards Under Small External Forces

. Consider a particle moving freely on the torus and colliding elastically with some fixed convex bodies. This model is called a periodic Lorentz gas, or a Sinai billiard. It is a Hamiltonian system with a smooth invariant measure, whose ergodic and statistical properties have been well investigated. Now let the particle be subjected to a small external force. This new system is not likely to have a smooth invariant measure. Then a Sinai-Ruelle-Bowen (SRB) measure describes the evolution of typical phase trajectories. We find general sufficient conditions on the external force under which the SRB measure for the collision map exists, is unique, and enjoys good ergodic and statistical properties, including Bernoulliness and an exponential decay of correlations.     

Direct particle motion and interaction modeling method applied to simulate propellant burn

A direct particle motion and particle interaction modeling method was developed to provide an alternative means of capturing the fundamental phenomena occurring during the burning of propellant grains. Individual propellant grains and other moving components are directly incorporated into the computational domain, removing the need for correlations for particle drag and interaction effects. The motion of the individual particles is calculated from the locally acting fluid induced and collision effect forces and moments. Particle/object interactions are handled through a soft particle collision algorithm. Localized mass and energy sources, accompanied by a shrinking particle size, simulate the effects of the combustion process.     

Numerical study of gas–solid flow in a cyclone separator

This paper presents a numerical study of the gas–powder flow in a typical Lapple cyclone. The turbulence of gas flow is obtained by the use of the Reynolds stress model. The resulting pressure and flow fields are verified by comparing with those measured and then used in the determination of powder flow that is simulated by the use of a stochastic Lagrangian model. The separation efficiency and trajectory of particles from simulation are shown to be comparable to those observed experimentally. The effects of particle size and gas velocity on separation efficiency are quantified and the results agree well with experiments. Some factors which affect the performance of cyclone were identified. It is shown that the collision between gas streams after running about a circle and that just entering occurred around the junction of the inlet duct and the cylinder of the cyclone, resulting in a short-circuiting flow. The combination of flow source and sink was distributed near the axis of cyclone, forming a flow dipole at axial section. Particles entering at different positions gave different separation efficiency. A particle with size exceeding a critical diameter, which was condition-dependant, would stagnate on the wall of cyclone cone. This was regarded as one of the main reasons for the deposition on the inner conical surface in such cyclones used in the cement industry.