Effect of exit location on flow of mice under emergency condition

The evacuation of crowds in a building has always emerged as a vital issue in many accidents. The geometrical structure of a room, especially the exit design has a great influence on crowd evacuation under emergency conditions. In this paper, the effect of exit location of a room on crowd evacuation in an emergency is investigated with mice. Two different exits are set in a rectangular chamber. One is located in the middle of a wall(middle-exit) and the other is at the corner of the chamber(corner-exit). Arching and clogging are observed in the flow of mice. The result based on the escape trajectories of mice shows a dynamic balance in the arch near the exit wherever the exit is located. We demonstrate that the occupant position in the arch has an effect on the escape sequence of mice. At a low stimulation level, the narrow middle-exit is more effective in increasing the flow rate of mice than the narrow corner-exit. However, the opposite result appears when the exit becomes wider. At a high stimulation level, the effect of exit location on flow of mice tends to be weakened. The results suggest that the specific level of stimulation needs to be taken into account when optimizing the evacuation efficiency of a crowd through the geometrical structure of a room.     

A numerical study of contact force in competitive evacuation

Crowd force by the pushing or crushing of people has resulted in a number of accidents in recent decades. The aftermath investigations have shown that the physical interaction of a highly competitive crowd could produce dangerous pressure up to 4500 N/m, which leads to compressive asphyxia or even death. In this paper, a numerical model based on discrete element method(DEM) as referenced from granular flow was proposed to model the evacuation process of a group of highly competitive people, in which the movement of people follows Newton's second law and the body deformation due to compression follows Hertz contact model. The study shows that the clogs occur periodically and flow rate fluctuates greatly if all people strive to pass through a narrow exit at high enough desired velocity. Two types of contact forces acting on people are studied. The first one, i.e., vector contact force, accounts for the movement of the people following Newton's second law. The second one, i.e., scale contact force, accounts for the physical deformation of the human body following the contact law. Simulation shows that the forces chain in crowd flow is turbulent and fragile. A few narrow zones with intense forces are observed in the force field, which is similar to the strain localization observed in granular flow. The force acting on a person could be as high as 4500 N due to force localization, which may be the root cause of compressive asphyxia of people in many crowd incidents.     

Simulating pedestrian flow through narrow exits

Introduction: The flow of pedestrians through narrow doorways is one of the most common features of crowd motions and evacuations. It is particularly an important aspect of pedestrian simulations models since their accuracy depends highly on their ability to produce realistic exit flow rates. The problem has been extensively studied in the literature, but many aspects of it have remained controversial with mixed (and often contradictory) evidence emerging from different studies and different methods. Methods: We discuss the significance of parameter calibration for accurate simulation of pedestrian flow through narrow exits using social force model. Based on sensitivity analyses, we show how simulated exit throughput rate can vastly differ by changing the value of certain parameters. We identify the two parameters that are most critical, and then calibrate them based on a set of experimental observations (at macro level). Using these calibrated parameters, we then re-examine three fundamental questions related to pedestrian flow at bottlenecks, (1) the relation between desired velocity and simulated egress time; (2) the effect of barricade at exits; and (3) the effect of exit in the corner versus the middle. Results: Our numerical analyses showed that, with the calibrated parameters, increasing the desired velocity in the social-force model results in monotonically shorter egress times (at a marginal rate that rapidly diminishes as the desired velocity increases). We showed that placing a panel-like barricade at exit can facilitate the outflow and reduces the egress time, but its effect depends on the widths of exit, as well as the size of the barricade and its distance to exit. We show that the positioning the exit in the corner is also effective in terms of reducing egress time, but only for very narrow exits. The benefit diminishes quickly as the exit becomes wider. Applications: These outcomes demonstrated the significance of parameter calibration for accurate simulation of crowd flows. The findings may also help to identify simple modifications that can facilitate crowd flows at narrow bottlenecks.     

Experiment and modeling of exit-selecting behaviors during a building evacuation

The evacuation process in a teaching building with two neighboring exits is investigated by means of experiment and modeling. The basic parameters such as flow, density and velocity of pedestrians in the exit area are measured. The exit-selecting phenomenon in the experiment is analyzed, and it is found that pedestrians prefer selecting the closer exit even though the other exit is only a little far. In order to understand the phenomenon, we reproduce the experiment process with a modified biased random walk model, in which the preference of closer exit is achieved using the drift direction and the drift force. Our simulation results afford a calibrated value of the drift force, especially when it is 0.56, there is good agreement between the simulation results and the experimental results on the number of pedestrians selecting the closer exit, the average velocity through the exits, the cumulative distribution of the instantaneous velocity and the fundamental diagram of the flow through exits. According to the further simulation results, it is found that pedestrians tend to select the exit with shorter distance to them, especially when the people density is small or medium. But if the density is large enough, the flow rates of the two exits will become comparable because of the detour behaviors. It reflects the fact that a crowd of people may not be rational to optimize the usage of multi-exits, especially in an emergency.     

Escape statistics for systems driven by dichotomous noise. I. General theory

Previous results on first-passage-time statistics for systems driven by dichotomous noise are extended in order to cover the escape from regions including fixed points of the stochastic flow. For such regions a treatment splitting the escape through one or the other boundary is required. The obtained escape probabilities and mean exit times are relevant for the complete characterization of stochastic systems undergoing bifurcations.     

Discrete element crowd model for pedestrian evacuation through an exit

A series of accidents caused by crowds within the last decades evoked a lot of scientific interest in modeling the movement of pedestrian crowds. Based on the discrete element method, a granular dynamic model, in which the human body is simplified as a self-driven sphere, is proposed to simulate the characteristics of crowd flow through an exit. In this model, the repulsive force among people is considered to have an anisotropic feature, and the physical contact force due to body deformation is quantified by the Hertz contact model. The movement of the human body is simulated by applying the second Newton's law. The crowd flow through an exit at different desired velocities is studied and simulation results indicated that crowd flow exhibits three distinct states, i.e., smooth state, transition state and phase separation state. In the simulation, the clogging phenomenon occurs more easily when the desired velocity is high and the exit may as a result be totally blocked at a desired velocity of 1.6 m/s or above, leading to faster-to-frozen effect.     

Escape Through a Small Opening: Receptor Trafficking in a Synaptic Membrane

We model the motion of a receptor on the membrane surface of a synapse as free Brownian motion in a planar domain with intermittent trappings in and escapes out of corrals with narrow openings. We compute the mean confinement time of the Brownian particle in the asymptotic limit of a narrow opening and calculate the probability to exit through a given small opening, when the boundary contains more than one. Using this approach, it is possible to describe the Brownian motion of a random particle in an environment containing domains with small openings by a coarse grained diffusion process. We use the results to estimate the confinement time as a function of the parameters and also the time it takes for a diffusing receptor to be anchored at its final destination on the postsynaptic membrane, after it is inserted in the membrane. This approach provides a framework for the theoretical study of receptor trafficking on membranes. This process underlies synaptic plasticity, which relates to learning and memory. In particular, it is believed that the memory state in the brain is stored primarily in the pattern of synaptic weight values, which are controlled by neuronal activity. At a molecular level, the synaptic weight is determined by the number and properties of protein channels (receptors) on the synapse. The synaptic receptors are trafficked in and out of synapses by a diffusion process. Following their synthesis in the endoplasmic reticulum, receptors are trafficked to their postsynaptic sites on dendrites and axons. In this model the receptors are first inserted into the extrasynaptic plasma membrane and then random walk in and out of corrals through narrow openings on their way to their final destination.     

Effect of varying two key parameters in simulating evacuation for a dormitory in China

Student dormitories are both living and resting areas for students in their spare time. There are many small rooms in the dormitories. And the students are distributed densely in the dormitories. High occupant density is the main characteristic of student dormitories. Once there is an accident, such as fire or earthquake, the losses will be cruel. Computer evacuation models developed overseas are commonly applied in working out safety management schemes. The average minimum widths of corridor and exit are the two key parameters affecting the evacuation for the dormitory. The effect of varying these two parameters will be studied in this paper by taking a dormitory in our university as an example. Evacuation performance is predicted with the software FDS + Evac. The default values in the software are used and adjusted through a field survey. The effect of varying either of the two parameters is discussed. It is found that the simulated results agree well with the experimental results. From our study it seems that the evacuation time is not in proportion to the evacuation distance. And we also named a phenomenon of “the closer is not the faster”. For the building researched in this article, a corridor width of 3 m is the most appropriate. And the suitable exit width of the dormitory for evacuation is about 2.5 to 3 m. The number of people has great influence on the walking speed of people. The purpose of this study is to optimize the building, and to make the building in favor of personnel evacuation. Then the damage could be minimized.     

Sizing of emulsion droplets under flow using flow-compensating NMR-PFG techniques

Using the nuclear magnetic resonance (NMR) pulsed field gradient (PFG) technique, it is possible to determine the size distribution of emulsion droplets. This method is extended so that the same measurements can be performed in the presence of flow. The resultant flow-compensating NMR-PFG technique is used to determine the oil droplet-size distribution of an oil-in-water emulsion flowing in a narrow tube at various flow rates. Comparison with the nonflowing oil droplet-size distribution enables the effect of velocity shear on the oil droplet-size distribution to be quantified.     

Simulation for pedestrian dynamics by real-coded cellular automata (RCA)

In this paper, we propose a new approach for pedestrian dynamics. We call it a real-coded cellular automata (RCA). The scheme is based on the real-coded lattice gas (RLG), which has been developed for fluid simulation. Similar to RLG, the position and velocity can be freely given, independent of grid points. Our strategy including the procedure for updating the position of each pedestrian is explained. It is shown that the movement of pedestrians in an oblique direction to the grid is successfully simulated by RCA, which was not taken into account in the previous CA models. Moreover, from simulations of evacuation from a room with an exit of various widths, we obtain the critical number of people beyond which the clogging appears at the exit.     

Langevin equation approach to granular flow in a narrow pipe

The gravity-driven flow of granular material through a rough, narrow vertical pipe is described using the Langevin equation formalism. Above a critical particle density the homogeneous flow becomes unstable with respect to short-wave length perturbations. In correspondence with experimental observations, we find clogging and density waves in the flowing material.     

Influences of exit and stair conditions on human evacuation in a dormitory

Evacuation processes of students are investigated by experiment and simulation. The experiment is performed for students evacuating from a dormitory with an exit and stairs. FDS+Evac is proposed to simulate the exit and stair dynamics of occupant evacuation. Concerning the exit and stair widths, we put forward some useful standpoints. Good agreement is achieved between the predicted results and experimental results. With the increase of exit width, a significant stratification phenomenon will be found in flow rate. Stratification phenomenon is that two different stable flow rates will emerge during the evacuation. And the flow rate curve looks like a ladder. The larger the exit width, the earlier the stratification phenomenon appears. When exit width is more than 2.0 m, the flow rate of each exit width is divided into two stable stages, and the evacuation times show almost no change. The judgment that the existence of stairs causes flow stratification is reasonable. By changing the width of the stairs, we proved that judgment. The smaller the width of BC, the earlier the stratification appears. We found that scenario 5 is the most adverse circumstance. Those results are helpful in performance-based design of buildings.     

Suppression of Rayleigh-Taylor instability by gyroviscosity and sheared axial flow in imploding plasma pinches

The synergistic stabilizing effect of gyroviscosity and sheared axial flow on the Rayleigh-Taylor instability in Z-pinch implosions is studied by means of the incompressible viscid magneto-hydrodynamic equations.The gyroviscosity(or finite Larmor radius) effects are introduced in the momentum equation through an anisotropic ion stress tensor.Dispersion relation with the effect of a density discontinuity is derived.The results indicate that the short-wavelength modes of the Rayleigh-Taylor instability are easily stabilized by the gyroviscosity effects.The long wavelength modes are stabilized by the sufficient sheared axial flow.However,the synergistic effects of the finite Larmor radius and sheared axial flow can heavily mitigate the Rayleigh-Taylor instability.This synergistic effect can compress the Rayleigh-Taylor instability to a narrow wave number region.Even with a sufficient gyroviscosity and large enough flow velocity,the synergistic effect can completely suppressed the Rayleigh-Taylor instability in whole wave number region.     

Spectral line narrowing in a gas by atoms trapped in a standing light wave

This paper presents results of a theoretical analysis of a new method for eliminating the Doppler broadening of spectral lines and the broadening by the transit time of atoms through a light beam. The atomic motion in a one-dimensional standing wave is studied and the conditions for translational-to-vibrational motion transformation are found. The variation in the Doppler contour by the trapping effect is investigated. It is illustrated, in particular, that the width of the narrow peak at the line centre depends mainly on the finite transit time of the atoms through the light beam. Next it is shown that, by accumulating slow atoms in a three-dimensional standing wave, it is possible, in principle, to observe narrow peaks with their widths determined only by the natural line width. The possibility of experimentally detecting of the phenomenon is discussed.     

Isotope dependence of widths of hole analog states

The isotope dependence of the widths of the hole analog states is studied for the Zr, Mo and Sn isotopes. In order to calculate the proton escape widths, we propose a microscopic model, in which the coupling of a neutron hole state to the isobaric analog state of the core is considered. It is found that the proton escape widths carry the observed isotope dependence of the widths of the hole analog states and that the isotope dependence of the proton escape widths is caused by two effects: the isotope dependence of the maximum available energy for a decaying proton, and that of the occupation probabilities of the excess neutron orbits in the parent state.     

Experimental measurements of two-dimensional planar propagating edge flames

The study of edge flames has received increased attention in recent years. This work reports the results of a recent study into two-dimensional, planar, propagating edge flames that are remote from solid surfaces (called here, “free-layer” flames, as opposed to layered flames along floors or ceilings). They represent an ideal case of a flame propagating down a flammable plume, or through a flammable layer in microgravity. The results were generated using a new apparatus in which a thin stream of gaseous fuel is injected into a low-speed laminar wind tunnel thereby forming a flammable layer along the centerline. An airfoil-shaped fuel dispenser downstream of the duct inlet issues ethane from a slot in the trailing edge. The air and ethane mix due to mass diffusion while flowing up towards the duct exit, forming a flammable layer with a steep lateral fuel concentration gradient and smaller axial fuel concentration gradient. We characterized the flow and fuel concentration fields in the duct using hot wire anemometer scans, flow visualization using smoke traces, and non-reacting, numerical modeling using COSMOSFloWorks. In the experiment, a hot wire near the exit ignites the ethane-air layer, with the flame propagating downwards towards the fuel source. Reported here are tests with the air inlet velocity of 25 cm/s and ethane flows of 967-1299 sccm, which gave conditions ranging from lean to rich along the centerline. In these conditions the flame spreads at a constant rate faster than the laminar burning rate for a premixed ethane-air mixture. The flame spread rate increases with increasing transverse fuel gradient (obtained by increasing the fuel flow rate), but appears to reach a maximum. The flow field shows little effect due to the flame approach near the igniter, but shows significant effect, including flow reversal, well ahead of the flame as it approaches the airfoil fuel source.     

Stadium型介观器件腔中粒子逃逸率的研究

本文研究了粒子在二维弱开口的Bunimovich Stadium型介观混沌器件中的逃逸规律.利用经典统计的方法,通过改变器件端口宽度、圆弧半径及器件腔长等参数,首次发现随器件各项参数变化的分形维数与粒子逃逸率趋势符合,并揭示了混沌体系的逃逸指数受器件形状的影响.统计并拟合了粒子逃逸率与粒子波数大小的关系,数值结果表明,粒子逃逸率与波数为二次函数关系,但逃逸率与能量大小不是严格的线性关系.进一步分析了在器件入口处粒子的衍射效应对粒子逃逸的影响,结果表明,衍射效应使粒子逃逸率增加,且粒子数的演化在时间较短时不再满足指数关系,长时间的演化再次满足指数衰减规律.     

Effects of closed immersion filtered water flow velocity on the ablation threshold of bisphenol A polycarbonate during excimer laser machining

A closed flowing thick film filtered water immersion technique ensures a controlled geometry for both the optical interfaces of the flowing liquid film and allows repeatable control of flow-rate during machining. This has the action of preventing splashing, ensures repeatable machining conditions and allows control of liquid flow velocity. To investigate the impact of this technique on ablation threshold, bisphenol A polycarbonate samples have been machined using KrF excimer laser radiation passing through a medium of filtered water flowing at a number of flow velocities, that are controllable by modifying the liquid flow-rates. An average decrease in ablation threshold of 7.5% when using turbulent flow velocity regime closed thick film filtered water immersed ablation, compared to ablation using a similar beam in ambient air; however, the use of laminar flow velocities resulted in negligible differences between closed flowing thick film filtered water immersion and ambient air. Plotting the recorded threshold fluence achieved with varying flow velocity showed that an optimum flow velocity of 3.00 m/s existed which yielded a minimum ablation threshold of 112 mJ/cm². This is attributed to the distortion of the ablation plume effected by the flowing immersion fluid changing the ablation mechanism: at laminar flow velocities Bremsstrahlung attenuation decreases etch rate, at excessive flow velocities the plume is completely destroyed, removing the effect of plume etching. Laminar flow velocity regime ablation is limited by slow removal of debris causing a non-linear etch rate over ‘n’ pulses which is a result of debris produced by one pulse remaining suspended over the feature for the next pulse. The impact of closed thick film filtered water immersed ablation is dependant upon beam fluence: high fluence beams achieved greater etch efficiency at high flow velocities as the effect of Bremsstrahlung attenuation is removed by the action of the fluid on the plume; low fluences loose efficiency as the beam makes proportionally large fluence losses at it passes through the chamber window and immersion medium.     

泡沫型干扰幕的光学衰减性能研究

泡沫型干扰幕是为解决多波段干扰领域有关问题研究的新技术。利用专用导弹综合测试系统,对其光学衰减性能进行了测试。一般只需几到几十厘米厚的干扰幕即可使得基于可见光、红外、激光的导弹制导系统失效,表明它对光传播具有明显的衰减作用,可以满足不同温度下不同目标干扰光学侦察与制导的作战使用要求。研究结论可为泡沫型干扰幕的战术运用设计提供必要的理论基础和实验依据。     

A computational study of asymmetric glottal jet deflection during phonation

Two-dimensional numerical simulations are used to explore the mechanism for asymmetric deflection of the glottal jet during phonation. The model employs the full Navier-Stokes equations for the flow but a simple laryngeal geometry and vocal-fold motion. The study focuses on the effect of Reynolds number and glottal opening angle with a particular emphasis on examining the importance of the so-called "Coanda effect" in jet deflection. The study indicates that the glottal opening angle has no substantial effect on glottal jet deflection. Deflection in the glottal jet is always preceded by large-scale asymmetry in the downstream portion of the glottal jet. A detailed analysis of the velocity and vorticity fields shows that these downstream asymmetric vortex structures induce a flow at the glottal exit which is the primary driver for glottal jet deflection.