肥皂泡破裂现象及产生小液滴分布研究

肥皂泡破裂产生液滴的大小和数目受破裂过程影响.本文研究了肥皂泡大小和高度对破裂产生液滴的影响,以及所产生液滴的分布规律.实验发现肥皂泡破裂产生的液滴在破裂高度较低时存在放射性线状分布现象;随着高度增加放射性线状分布消失;同时分析了肥皂泡破裂产生液滴的数目及肥皂膜的厚度随肥皂泡体积的变化规律.结果表明,肥皂泡体积和液滴数目之间存在幂函数关系,理想情况下肥皂膜厚度与碎片数目之间也存在幂函数关系.肥皂泡破裂过程中产生的液滴可以按照拟合结果大致分为小碎片,中等碎片和大碎片,它们分别对应于肥皂泡破裂过程的3个变化阶段.     

考虑在能见度受限下行人跟随行为特性的建模与模拟

研究了行人在能见度受限情况下的疏散行为,考虑行人对环境的熟悉程度,将行人分为熟悉环境人群和不熟悉环境人群.对于房间内熟悉环境的行人,改进势函数元胞自动机模型来模拟其疏散行为.对于不熟悉环境人群,分析其在视野范围内的跟随行为,并制定了不同跟随行为策略,来研究其跟随行为特性.仿真模拟了房间内熟悉环境人群的人数占比、房间内的视野半径大小以及行人密度等参数,研究其对行人疏散的影响,比较不熟悉环境人群采取的跟随策略的优劣.发现疏散时间的大小与房间内视野半径的大小和房间内熟悉环境者密度的大小有关.其次,跟随策略的有效性与视野半径的大小和熟悉环境者密度有关.而且在单一策略环境下,有着同样的规律.这些发现能对大型公共场所如超市、体育馆的应急疏散情况提供一些启示,有助于在视野受限情况下制定一些有效的指导策略.     

碰撞聚合引起液滴数目变化的生灭过程模型

液滴碰撞聚合是气体/液滴两相流动中的重要现象.为研究碰撞聚合引起的液滴数目变化,考虑液相仅包含大小两类尺寸液滴的情形,计算不同尺寸的两个液滴间的碰撞概率,对固定观察区域内液滴的碰撞聚合、迁入及迁出因素作随机分析,建立描述液滴数目变化的生灭过程模型.由无条件概率模型方程,得出模型方程的相应平稳分布.以雨滴下落过程的质量增长为例,说明所得分布在气体液滴两相流动中的应用.     

改进的DLA方法模拟薄膜二维生长

对经典的DLA模型进行改进，研究了薄膜的二维生长过程.通过改变表征吸附原子在基底扩散 能力的参量D_T，D_C以及表征沉积速率的参量D_V，得到 了与实验一致的薄 膜分形生长模式和团状生长模式.分析了薄膜的形核阶段原子团的大小分布，以及不同条件 下原子团的数目和大小随覆盖度的变化. 关键词： DLA 薄膜生长 分形生长 团状生长     

脆性断裂的统计理论

本文试图从位错理论出发来探索晶体脆性断裂的统计理论。脆性断裂过程,实质上是微裂缝在极小的范性形变过程中形成长大和传播的随机过程。本文导出了描述这种随机过程的微分方程,利用微裂缝形成长大的位错机理,解出了微裂缝大小的统计分布函数。文中给出了范性形变、加工硬化和活动位错源数目与微裂缝数目和大小之间的函数关系。过去研究脆性断裂时,范性变形只是含糊地包括在有效表面能之内,而加工硬化和活动位错源数目则一向被略去。从微裂缝大小的统计分布函数和微裂缝的传播条件,导出了强度的统计分布函数,从而求得了脆性断裂判别式、脆性断裂强度及脆性-范性转变温度。     

加压条件下流体分子聚集体形成的探究

一、分子聚集理论简介 分子聚集理论认为任何物质中均存在分子聚集现象而分子的这种聚集行为是由分子间的范德华力(色散力、诱导力和定向力)及氢键力所致。任何体系均由数目不等,大小不同的聚集体组成;聚集体的数目按一定规律分布。物质的分子聚集度不仅与分子大小形状     

包含轻子结构的夸克模型

对标准模型作手征性扩充后,模型中平行地存在手征性相反的夸克态.相应于构成强子的f代普通夸克,新加的同样代数、手征性相反的夸克可能构成轻子.对扩充后的模型超对称化之后,使得渐近自由性质的破坏所要求的代的数目从大于33/8减少到大于9/4,从而有可能解释手征相反的夸克构成的轻子为什么比普通夸克构成的强子大小要小得多等特点.     

正常和嵌合肿瘤乳腺温度分布特征的有限元分析

基于乳腺解剖学结构和生理学特征,建立了适合应用于正常和嵌合肿瘤乳腺三维热传递的分析模型.该模型综合考虑了乳腺代谢产热、血液灌注和动静脉血管与乳腺组织之间的热交换等因素对温度场的影响.数值研究了正常和嵌合肿瘤乳腺的温度分布特征,着重分析代谢产热、血液灌注率、乳腺肿瘤的大小、位置与数目以及空气对流系数、环境温度等因素对乳腺温度分布的影响.结果表明:血液灌注率、代谢产热、乳腺肿瘤的大小、位置与数目对乳腺温度分布特征的影响明显;环境条件对嵌含肿瘤乳腺的体表温度分布影响较大.研究结果将有助于指导乳腺红外热图像的实验并为其定性分析提供重要的参考.     

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对等离子体气动激励控制边界层进行了数值仿真。将等离子体气动激励对边界层的作用建模成动量和热量。通过由基于表面放电的二维流体体力模型得到的等离子体气动激励的体力分布函数,得到向边界层注入的动量和热量分布,将动量和热量以源项的形式引入N-S方程求解。研究了等离子体气动激励的强度、激励电极的数目、来流速度的大小以及热量项的大小对等离子体气动激励作用效果的影响,仿真结果与实验一致。     

二维超导薄膜中拓扑缺陷数目与冷却速度关系研究

基于含时Ginzburg-Landau（TDGL）方程建立二维超导薄膜经历快速冷却后的拓扑缺陷数目与冷却速度的关系模型.采用差分法对此模型进行了数值模拟,计算出不同冷却速度下拓扑缺陷数目随着时间的变化关系.计算结果发现,在不同冷却速度下,缺陷数目随着时间的变化可以分为两个阶段：第一阶段缺陷数目较多,拓扑缺陷数目随时间急...     

Abnormal crowd behavior detection by using the particle entropy

The crowd distribution information is the crucial information for abnormal behaviors detection in the crowd scenes. In this paper, we firstly refer to the definition of the entropy and propose an algorithm effectively and accurately representing the crowd distribution information in the crowd scenes. The proposed algorithm not only avoids unstable foreground extraction, but also owns low computational complexity. To detect the abnormal crowd behaviors, we use the Gaussian Mixture Model (GMM) over the normal crowd behaviors to predict the abnormal crowd behaviors since GMM usually can deal well with the unbalanced problem. In this paper we simultaneously use the crowd distribution information and the crowd speed information to estimate the parameters of GMM over the normal crowd behaviors and predict abnormal crowd behaviors. Experiment conducted on publicly available dataset consisting of gathering and dispersion events validates that the proposed approach can preeminently reflect the crowd distribution information. In addition, experiments conducted on publicly UMN dataset demonstrate that the proposed abnormal crowd behavior detection method has an excellent performance and outperforms the state-of-the-art methods.     

Microscopic information processing and communication in crowd dynamics

Due, perhaps, to the historical division of crowd dynamics research into psychological and engineering approaches, microscopic crowd models have tended toward modelling simple interchangeable particles with an emphasis on the simulation of physical factors. Despite the fact that people have complex (non-panic) behaviours in crowd disasters, important human factors in crowd dynamics such as information discovery and processing, changing goals and communication have not yet been well integrated at the microscopic level. We use our Microscopic Human Factors methodology to fuse a microscopic simulation of these human factors with a popular microscopic crowd model. By tightly integrating human factors with the existing model we can study the effects on the physical domain (movement, force and crowd safety) when human behaviour (information processing and communication) is introduced.In a large-room egress scenario with ample exits, information discovery and processing yields a crowd of non-interchangeable individuals who, despite close proximity, have different goals due to their different beliefs. This crowd heterogeneity leads to complex inter-particle interactions such as jamming transitions in open space; at high crowd energies, we found a freezing by heating effect (reminiscent of the disaster at Central Lenin Stadium in 1982) in which a barrier formation of naïve individuals trying to reach blocked exits prevented knowledgeable ones from exiting. Communication, when introduced, reduced this barrier formation, increasing both exit rates and crowd safety.     

Agent-based modeling of a multi-room multi-floor building emergency evacuation

Panic during emergency building evacuation can cause crowd stampede, resulting in serious injuries and casualties. Agent-based methods have been successfully employed to investigate the collective human behavior during emergency evacuation in cases where the configurational space is extremely simple–usually one rectangular room–but not in evacuations of multi-room or multi-floor buildings. This implies that the effect of the complexity of building architecture on the collective behavior of the agents during evacuation has not been fully investigated. Here, we employ a system of self-moving particles whose motion is governed by the social-force model to investigate the effect of complex building architecture on the uncoordinated crowd motion during urgent evacuation. In particular, we study how the room door size, the size of the main exit, the desired speed and the friction coefficient affect the evacuation time and under what circumstances the evacuation efficiency improves.     

大空间人群声学模型

经典扩散声场理论难以适用于大空间建筑。为了探究大空间建筑中人群分布对声场的影响,本文用模拟与实测相结合的方法,提出了一种适用于大空间的人群声学模型,得到了确定等效声源和人群声源的简化方法,以及人群密度与声压级之间、人群总数与发声人数之间的关系。用实测数据对该人群声学模型进行了验证。     

A novel approach for crowd video monitoring of subway platforms

Crowd monitoring in a dense crowd scene has become an important and challenging topic in the field of video surveillance system. This paper proposes a novel crowd monitoring approach for subway platforms to address requirements in rail traffic management. Firstly, an improvement for Mixture Gaussian background modeling is presented to segment the crowd. In the process of feature extraction, the concept of the weighted area is proposed to solve the problem of the perspective of images. To deal with the issue of the occlusion between individuals, an improved gradient feature is developed in this paper. And then, Adaptive Boost classifier with the feature weighted area and the improved gradient is used to estimate the crowd density. Finally, the crowd is counted by the method of linear regression. The experimental results show that the proposed approach is feasible and effective for crowd monitoring in real subway platforms.     

Macroscopic effects of microscopic forces between agents in crowd models

Crowd scenarios have attracted attention from computer modellers, perhaps because of the impracticality of studying the phenomenon by traditional experimental methods. For example, Kirchner has proposed an agent-based crowd model inspired by fields of elementary particles [A. Kirchner, A. Schadschneider, Simulation of evacuation processes using a bionics-inspired cellular automaton model for pedestrian dynamics, Physica A 312 (2002) 260–276.], but chose not to incorporate crowd forces. We argue that crowd forces (and associated injuries) are an essential characteristic of crowds, and that their omission will negatively affect the model's ability to make predictions (e.g. time for a crowd to pass through an exit). To support this position we describe an evolution of Kirchner's model that includes a vector-based particle field to represent forces. We show qualitative and quantitative differences compared to Kirchner's model when force is included. The Swarm Force model demonstrates—by showing non-linear effects of force—the necessity of force in crowd models.     

Conflict game in evacuation process: A study combining Cellular Automata model

The game-theoretic approach is an essential tool in the research of conflicts of human behaviors. The aim of this study is to research crowd dynamic conflicts during evacuation processes. By combining a conflict game with a Cellular Automata model, the following factors such as rationality, herding effect and conflict cost are taken into the research on frequency of each strategy of evacuees, and evacuation time. Results from Monte Carlo simulations show that (i) in an emergency condition, rationality leads to “vying” behaviors and inhibited “polite” behavior; (ii) high herding causes a crowd of high rationality (especially in normal circumstances) to become more “vying” in behavior; (iii) the high-rationality crowd is shown to spend more evacuation time than a low-rationality crowd in emergency situations. This study provides a new perspective to understand conflicts in evacuation processes as well as the rationality of evacuees.     

The effect of individual tendency on crowd evacuation efficiency under inhomogeneous exit attraction using a static field modified FFCA model

As an extension of the Asymmetric Simple Exclusion Process, the floor field cellular automata model has its specific advantages in reproducing crowd self-organized phenomena, embodying individual characteristics and reducing the computing complexity by translating the long-ranged interaction to local interaction. Evacuation from a room is an important part in the study of building evacuation. In our experiment and real life observation we found the exit attraction non-uniformity. To obtain the effect of individual tendency to the exit attraction center on the crowd evacuation efficiency, the static field is modified. Compared with the control group, the exit attraction non-uniformity has a disadvantage in the crowd evacuation efficiency. The position deviation between the exit geometric center and the exit attraction center delays the crowd evacuation by generating a local merging flow. In addition, the individual tendency also increases the crowd evacuation time by increasing the static field gradient to the attraction center, leading to a low usage efficiency of exits. Compared with the influence of other factors, the inhomogeneous exit attraction has an obvious effect on the crowd evacuation efficiency.     

Dynamics of emotional contagion in dense pedestrian crowds

In places with high-density pedestrian movements, irrational emotions can quickly spread out under emergency, which may eventually lead to asphyxiation and crushing. It was noticed that a pedestrian's emotion in crowd would change as a result of the influence from other pedestrians. Thus, to explore the dynamics of emotion contagion process in dense pedestrians, two types of pedestrian emotions, i.e., negative and positive have been identified. Taking into account the emotional transit of a pedestrian, a crowd movement model is established in the present paper. We simulate pedestrian movement in a region with periodic boundary condition to study the dynamics of emotional contagion in dense crowds. Influences of the initial negative pedestrian proportion, pedestrian crowd density, emotion influence radius, and dose factor on the transition of overall crowd emotion state have been investigated. We expect this study could provide theoretical suggestions for crowd management.     

Modelling crowd–bridge dynamic interaction with a discretely defined crowd

This paper presents a novel method of modelling crowd–bridge interaction using discrete element theory (DET) to model the pedestrian crowd. DET, also known as agent-based modelling, is commonly used in the simulation of pedestrian movement, particularly in cases where building evacuation is critical or potentially problematic. Pedestrians are modelled as individual elements subject to global behavioural rules. In this paper a discrete element crowd model is coupled with a dynamic bridge model in a time-stepping framework. Feedback takes place between both models at each time-step. An additional pedestrian stimulus is introduced that is a function of bridge lateral dynamic behaviour. The pedestrians' relationship with the vibrating bridge as well as the pedestrians around them is thus simulated. The lateral dynamic behaviour of the bridge is modelled as a damped single degree of freedom (SDoF) oscillator. The excitation and mass enhancement of the dynamic system is determined as the sum of individual pedestrian contributions at each time-step. Previous crowd–structure interaction modelling has utilised a continuous hydrodynamic crowd model. Limitations inherent in this modelling approach are identified and results presented that demonstrate the ability of DET to address these limitations. Simulation results demonstrate the model's ability to consider low density traffic flows and inter-subject variability. The emergence of the crowd's velocity–density relationship is also discussed.