球形纳米颗粒Brown凝并碰撞效率的新表达式

研究了邻苯二甲酸二辛酯纳米颗粒在Brown凝并过程中的碰撞效率．在考虑Stokes阻力、润滑力、van der Waals力和颗粒变形恢复力的情况下推导了一组碰撞方程,通过数值求解这组方程,得到了当颗粒半径从50 nm到500 nm变化时,颗粒碰撞效率和半径之间的关系,计算得到的结果和实验结果符合较好．计算结果表明,在颗粒半径为50 nm到500 nm的情况下,颗粒的碰撞效率随颗粒半径的增加而减小．基于计算结果,提出了颗粒碰撞效率的新表达式．     

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．     

带有弹性碰撞的离散的凝结方程

带有弹性碰撞的离散的凝结方程是反映粒子增长动力学的数学模型，它刻划了这样一种粒子反应系统；系统中任意两个粒子碰撞后一定的概率或者凝结成为更大的粒子，或者发生弹性碰撞．本文研究了这一系统发生冻肢的可能性，并给出了一个充分条件．     

基于浸入边界-有限元法的流固耦合碰撞数值模拟方法

针对流固耦合碰撞问题,建立了流体中固体与固体碰撞界面解析直接模拟方法,采用清晰界面浸入边界法模拟流体中的动边界问题,避免了传统贴体网格方法在求解流体中存在固体间碰撞问题时网格出现负体积的问题,采用基于罚函数的有限元方法对固体的运动和碰撞进行求解,以分域耦合方式实现流体域和固体域的耦合求解.通过与静止流体中球形颗粒与壁面正碰撞和斜碰撞的实验数据对比,验证了建立的数值模拟方法对流体中固体与固体碰撞数值模拟的正确性,获得了流体域流场在碰撞前后随时间的变化,同时通过该文建立的数值模拟方法也获得了固体域中固体的碰撞力和应力.未来,将把该数值模拟方法应用到流体流动环境中,如固体颗粒对管道的冲蚀、流体诱导海洋立管之间的碰撞、坠物对海底管道的撞击等.     

Cs-Sr系统中激光感生非弹性碰撞过程的数值研究

利用已建立的四能级理论模型对提出的Cs Sr中的两个激光感生碰撞过程进行了数值计算 ,得到了碰撞跃迁几率随碰撞参数的变化关系及碰撞截面随转换激光失谐量的变化关系 ,并与三能级近似理论模型的计算结果进行了比较 .通过比较四能级理论与三能级近似理论模型的计算结果 ,进一步证实了理论的分析 :当 |ω_{2 1}|值与 |ω₄₃ |相近时 ,三能级理论的计算结果将存在着很大的误差 ,而四能级理论模型则适合于计算各种条件下的激光感生碰撞过程 .     

基于嵌套网格的环空流体内旋转杆柱与井筒碰撞特性研究北大核心CSCD

针对浸没在流体中杆管柱间相互接触问题,基于嵌套网格技术,该文建立了环空流体内旋转杆柱与井筒间碰撞的数值求解方法.将环空流体域分为相互嵌套的子区域:背景网格和组件网格,推导了各嵌套区域流场边界传递信息的插值计算公式,采用分域方法对环空流体域与杆柱固体域耦合进行求解.通过静止流体中球形颗粒与壁面正、斜碰撞实验对比,验证该文数值方法的正确性.研究了不同流体黏度、杆柱旋转速度条件下杆柱与井筒的碰撞特性,结果表明:1)杆柱与井筒碰撞的碰撞力、速度随黏度增大而降低,即杆柱与井筒碰撞的剧烈程度与流体黏度负相关;2)随着杆柱旋转速度增大,杆柱与井筒的碰撞力、速度也增大,即杆柱与井筒碰撞的剧烈程度与转速正相关.     

求解考虑颗粒凝并的通用动力学方程的多重MonteCarlo算法

Monte Carlo(MC)方法被广泛用于通用动力学方程的求解,然而普通MC方法的计算代价较高而计算精度不稳定．提出一种新的多重Monte Carlo(MMC)算法来求解GDE,该算法同时具有基于时间驱动MC方法、常数目法和常体积法的特点．首先详细介绍了该算法,包括加权虚拟颗粒的引入,MMC算法的计算流程,时间步长的设置,颗粒是否发生凝并事件的判断,凝并伙伴的寻找,凝并事件的后果处理．然后利用MMC算法对存在理论分析解的5种特殊工况进行数值求解,模拟结果与理论解符合很好,证明MMC算法具有良好的计算精度和较低的计算代价．最后分析了不同类型的凝并核对于凝并过程的影响,常凝并核和连续区布朗凝并核对小颗粒影响大一些,而线性凝并核和二次方凝并核对大颗粒影响大一些．     

158 A Ge V p-Pb Pb-Pb碰撞中的单奇异和多奇异粒子产生

用描写相对论性核 核碰撞的LUCIAE模型及相应的MonteCarlo事例产生器分析了WA97最近发表的 1 5 8AGeVp Pb和Pb Pb碰撞中单奇异粒子 (Λ ,Λ)和多奇异粒子 (Ξ-,Ξ-,Ω-,Ω-)的多重数和横质量分布 .由于LUCIAE模型包含了弦碎裂微观过程中奇异夸克压低因子随碰撞体系的能量、中心度和质量的增大而增大 ,以及由它导致的相对论性核 核碰撞宏观过程中奇异粒子产额随上述三因素之增而增的物理机制 ;LUCIAE模型计算结果能较好描写WA97实验所揭示的相对论性核 核碰撞中奇异粒子产额随中心度之增而增和奇异粒子增强随奇异夸克数之增而增的实验事实 ,以及单奇异和多奇异粒子的横质量分布 .     

吸水体膨颗粒与油藏适应性评价

针对矿场调剖实际需求,利用仪器检测和物理模拟方法,开展了体膨颗粒吸水率与溶胀率、抗剪切性、渗流特性、传输运移能力、粒径与油藏孔隙匹配关系和驱油效果实验研究.结果表明:随时间延长,体膨颗粒吸水率和溶胀率增大,并且初期增幅较大,24小时后增幅减缓.体膨颗粒抗剪切性能较好,经地层剪切后83%以上仍为大颗粒.体膨颗粒粒径愈小,溶剂水矿化度愈低,吸水率和溶胀率愈大,抗剪切能力愈差;与污水相比较,污水配置聚合物溶液中体膨颗粒吸水率和溶胀率较小,抗剪切性较好,当体膨颗粒浓度为6000mg/L时,"体膨颗粒粒径/平均喉道直径"范围在4.18~5.40之间可适用于油藏.推荐体膨颗粒浓度6000mg/L,注入量0.38PV,调剖半径51.3m,为避免封堵近井地带,可先选择小粒径颗粒注入,并逐渐增大粒径.     

三氧化二铝液滴对心碰撞直接数值模拟

为研究固体火箭发动机内三氧化二铝液滴碰撞的物理规律及结果预测模型,针对两个相同尺寸的三氧化二铝液滴对心碰撞,开展了直接数值模拟.首先进行了正十四烷液滴在氮气环境下的对心碰撞数值研究,数值与实验结果基本一致,验证了计算方法的可行性及准确性.针对三氧化二铝液滴开展了6 MPa压强下不同Weber数的对心碰撞数值研究,计算Weber数范围为10~200,Ohnesorge数为0.036 4;获得了反弹、大变形后聚合和自反分离3种结果类型,反弹与大变形后聚合的临界分离Weber数为26,大变形后聚合与自反分离的临界分离Weber数为44.根据临界Weber数对其他流体液滴碰撞模型进行修正,可以获得三氧化二铝液滴的碰撞模型.     

Collision avoidance for nonrigid objects

Summary The path existence problem and the collision detection problem for time-varying objects in a geometric scene are discussed. For a large class of spherical nonrigid objects, exact solutions of the path existence problem are developed based on decomposition techniques and graph traversal. For the collision detection problem of a single moving circle in the plane, efficient data structures are presented for linear/circular and polynomial paths.Work was partially supported by DFG (Mu744/1-1).     

液滴碰撞和聚合模型研究

建立了描述液滴碰撞和聚合过程的数学模型,设计了一种高效的计算液滴碰撞对搜索算法,并在已有研究成果的基础上对液滴碰撞的结果做了进一步的发展．借助平滑粒子流体动力学方法两种实现方式各自的优点,将液滴间的相互作用局限在其周围一定数目的液滴之间,并采用积分核函数定义了液滴间碰撞的概率,通过数值模拟探讨了模型的特性．结果表明,所建模型对所采用的计算网格没有明显的依赖性,具有较高的计算精度和计算效率,不但能很好地维持系统动量的守恒性,而且对液滴初始尺寸分布没有明显的依赖性．     

Collision detection for deforming necklaces

In this paper, we propose to study deformable necklaces—flexible chains of balls, called beads, in which only adjacent balls may intersect. Such objects can be used to model macro-molecules, muscles, ropes, and other linear objects in the physical world. We exploit this linearity to develop geometric structures associated with necklaces that are useful for collision detection in physical simulations. We show how these structures can be implemented efficiently and maintained under necklace deformation. In particular, we study a bounding volume hierarchy based on spheres which can be used for collision and self-collision detection of deforming and moving necklaces. As our theoretical and experimental results show, such a hierarchy is easy to compute and, more importantly, is also easy to maintain when the necklace deforms. Using this hierarchy, we achieve a collision detection upper bound of O(nlogn) in two dimensions and O(n^2−2/d) in d-dimensions, d3. To our knowledge, this is the first subquadratic bound proved for a collision detection algorithm using predefined hierarchies. In addition, we show that the power diagram, with the help of some additional mechanisms, can be used to detect self-collisions of a necklace in a way that is complementary to the sphere hierarchy.     

Collision computation of moving bodies

In this paper, an explicit mathematical representation of n-dimensional bodies moving in translation along general trajectories is derived. This representation is used to find out if two moving bodies are going to collide. An optimization problem is developed for finding the time and location of collision. We consider the special cases of linear and piece-wise linear trajectories. The collision in this case can be obtained by solving a linear program or a sequence of linear programs, respectively. The problem of finding the collision time and location of several moving bodies is cast as an integer programming problem. A comprehensive simulation study shows that this approach requires much lesser computation time when compared with the current approach of finding the collision between all pairs of bodies.     

Collision Detection Using Interpolation Schemes

An algorithm using interpolation methods for the efficient search of the collision time and state of planar bodies is presented. Using interpolation and directed distances, the algorithm can efficiently obtain information about the collision. Further, a simulation system for multiple bodies is investigated and for some simple examples comparisons are shown of the proposed method and a traditional approach.     

A Ship Collision Model for Overtaking

This paper describes a mathematical model of a ship being overtaken by another vessel on a parallel track. Graphs are presented which give the minimum safe overtaking distance for any given situation. The length of time for which a ship is exposed to danger and the probability of collision during an overtaking encounter are examined. Results show that at sea in fog, ships often overtake dangerously close.     

Collision Avoidance in Bi-Directional AGV Systems

The use of a bi-directional, as opposed to a one-way, transportation system, can increase the operational efficiency of automated guided vehicles in both manufacturing and warehousing environments. However, the full potential will only be realized if the routeing algorithms pay particular attention to the problem of collision avoidance. This paper is concerned with the development of such an algorithm. The method is based on the use of delays and deviations to avoid collisions that could arise when using the shortest routes for each vehicle, and is applicable to any transportation system which can be represented as a network with known travel times.     

Collision of Almost Parallel Vortex Filaments

We investigate the occurrence of collisions in the evolution of vortex filaments through a system introduced by Klein, Majda, and Damodaran and Zakharov . We first establish rigorously the existence of a pair of almost parallel vortex filaments, with opposite circulation, colliding at some point in finite time. The collision mechanism is based on one of the self‐similar solutions of the model, described by the authors in an earlier work. In the second part of this paper we extend this construction to the case of an arbitrary number of filaments, with polygonal symmetry, that are perturbations of a configuration of parallel vortex filaments forming a polygon, with or without its center, rotating with constant angular velocity.© 2016 Wiley Periodicals, Inc.     

On Collision Invariants for Linear Scattering

In this article, we extend the result of Boltzmann on the characterization of collision invariants from the case of hard disks to a class of two‐dimensional compact, strictly convex particles.© 2018 Wiley Periodicals, Inc.