Fan Weicheng

Simulation of bi-direction pedestrian movement using a cellular automata model

A cellular automata model is presented to simulate the bi-direction pedestrian movement. The pedestrian movement is more complex than vehicular flow for the reason that people are more flexible than cars. Some special technique is introduced considering simple human judgment to make the rules more reasonable. Also the custom in the countries where the pedestrian prefer to walk on the right-hand side of the road are highlighted. By using the model to simulate the bi-direction pedestrian movement, the phase transition phenomena in pedestrian counter flow is presented. Furthermore, the introduction of back stepping breaks the deadlock at the relatively low pedestrian density. By studying the critical density of changing from freely moving state to jammed state with different system sizes and different probabilities of back stepping, we find the critical density increases as the probability of back stepping increases at the same system size. And with the increasing system size, the critical density decreases at the same probability of back stepping according to the scope of system size studied in this paper.

Self-organized criticality of forest fire in China

Self-organized criticality (SOC) of forest fire is studied from an analysis of a large series of forest-fire records from 1950 to 1989 in China. The time-invariant, scale-invariant characteristics of SOC of forest fire in China are analyzed in detail. The deviations between the occurrence frequency of very large fires and the power-law relation are explained by the forest-fire model with tree immunity (FFMTI). Actual forest-fire records are compared with the simulation results of a self-organized critical forest-fire model. It is shown that the forest-fire model applies well to explain the SOC characteristics of a forest fire. SOC characteristics have practical implications on forest-fire protection.

Experimental Study on the Effectiveness of the Extinction of a Pool Fire with Water Mist

In order to study the effectiveness of the extinction of a pool fire with one nozzle water mist, a series of experiments were conducted under different conditions in an open space. Fire sources are small-scale circular stainless steel pans of 130 and 200 mm in diameter with the fuel of alcohol and kerosene. Before and after the application of water mist, some K-type thermocouples along the pool centerline and a digital camera were used to measure the flame temperature and visualize the process of the fire extinction. A thermogage and a turbine flux sensor were used to measure the flame radiant heat flux and the application rate of water, respectively. A Particle Image Velocimetry and Sizing (PIVS) technique was developed to characterize the water mist. The experimental results show that both the flame of alcohol and kerosene cannot be extinguished in many cases when the pressure is lower than 0.4 MPa. In addition, the distance between the flame and the nozzle, and the application rate of water are two main factors which influence the effectiveness of the extinction of a pool fire when the working pressure is lower and the impulse injection of water mist can improve the effectiveness of fire extinction. However, it should be noted that the results are limited to the experimental conditions because it is still difficult to get the functional relationships of pool fire extinction mechanisms with water mist.

Fire situation and fire characteristic analysis based on fire statistics of China

This paper describes the fire situation of China in 1998. Fire statistics data have been analyzed with a view to understand the characteristics of fire accidents, including vocation and location distribution, cause analysis, monthly frequency and frequency of fires by time of day etc. It is revealed that specific work on fire protection should be taken so as to meet the demands of the society. In addition, some of the major fire accidents are also recapitulated briefly. Finally, the study highlights the importance to carry out fire statistics and gives some suggestions.

Preliminary Study on the Interaction of Water Mist with Pool Fires

In this paper, some preliminary measurements and observations were conducted to investigate the interaction of water mist with pool fires. The fire source is a small-scale circular stainless steel pan with heptane, ethanol and kerosene as fuel. Water mist was generated by a downward-directed pressure nozzle that was positioned on a square steel plate 300 mm over the fuel sample and was operated at pressures of 0.5 MPa. The water mist characteristics were determined by a LDV/APV system. The radiation spectra of the flames were measured by a monochromator and the radiant heat flux was obtained by a thermogage before and after application of water mist. Thermography was used to visualize the thermal field of the flame. The experimental results show that the interaction mechanisms of kerosene flame are different from those of ethanol and heptane.

Modeling Occupant Evacuation using Cellular Automata - Effect of Human Behavior and Building Characteristics on Evacuation

This paper presents a microdiscrete evacuation model which emphasizes the human behavior and is focused on studying the generic properties of occupant evacuation from crowded large, open spaces after a fixed premovement stage. By using Cellular Automata (CA) in developing the rules, the model achieves the advantages of effectively capturing the behavior of occupants at the individual-level while attaining realistic collective level activity. The lively demonstration of the evacuation process offers an easy examination of occupant movement on computer. The studies on some important characteristics in evacuation such as the existence of different velocities of people and the different structure of building offer some key factors affecting evacuation efficiency. By studying on evacuation from a corridor, with and without widen part, we found disordered moving states will badly decrease the evacuation efficiency. It enables us to understand the special phenomena in evacuation and is helpful in performance-based building design.

Study of Liquid Pool Fire Suppression with Water Mists by Cone Calorimeter

An experimental study of the pool fire suppression with water mists was performed in this paper. Spatially resolved droplet size, velocity distributions, and volume flux of the fine water mist has been obtained by LDA/APV system. A method to correct for the presence of droplets is presented and used to determine the heat release rate using a cone calorimeter system, the effects of water mist application on the heat release rate for liquid pool fires were studied. It was found that the volume flux of the water spray mostly determined the liquid pool fire-behavior. For the current experimental conditions, the flame was enlarged when lower volume flux of water is used, and suppressed significantly when higher volumes of water are used. Two opposing mechanisms compete when water mists are applied, which is more complex than the halon agents, such as 1301. The combustion enhancement becomes insignificant when water mists with the proper characteristics such as adequate volume flux are applied to the diffusion flame in a confined space.

Experimental Study on Cooling a Hot Solid Surface with Water Mist

In this paper, a series of experiments are performed to investigate the hot solid surface cooling with water mist under different conditions, such as different initial surface temperatures and mist characteristics (droplet size, droplet velocity, etc.), while these parameters are simultaneously varied. A 150 150 10mm 3chrome-plated stainless steel plate is heated from below by a 1500-W electric cooker continuously. A downward pressure nozzle is positioned on a square steel plate, 1000mm above the surface to inject water mist, the 0.5mm K-type thermocouples are jointed on the surface to obtain its temperature, and a TVS-2000ST Thermography is used to visualize the transient thermal behavior of a water mist and obtain the temperature distribution of the surface. The characteristics of the water mist are obtained by a modified PIVS (Particle Image Velocimetry and Sizing) technique previously. Based on the experiments, the effects of mist parameters and the initial surface temperature on droplet evaporative cooling are analyzed. Further discussion is carried out by considering the relationship between these parameters and the droplet Weber number, the results show that an inverse relationship between the cooling efficiency and mist droplet Weber number existed in this study.

Experimental Study on Spontaneous Ignition of Wood Exposed to Variable Heat Flux

The ignition of combustible materials is an important process in a fire incident. In this work, an experimental study on the ignition process of wood exposed to a variable heat flux has been carried out. Increasing heat flux is adopted and adjusted to simulate a practical fire environment. The time to ignition, temperature distribution, and mass loss are measured for two species of wood. Both, the increasing rate of incident heat flux and the properties of wood, especially density, obviously affect the results. A conduction model is developed to calculate the surface temperature. A compound ignition criterion is brought out for a variable heat flux.

An improved cross-correlation method for (digital) particle image velocimetry

An improved method that brings enhancement in accuracy for the interrogation of (digital) PIV images is described in this paper. This method is based on cross-correlation with discrete window offset, which makes use of a translation of the second interrogation window and rebuilds it considering rotation and shear. The displacement extracted from PIV images is predicted and corrected by means of an iterative procedure. In addition, the displacement vectors are validated at each intermediate of the iteration process. The present improved cross-correlation method is compared with the conventional one in accuracy by interrogation of synthetic and real (digital) PIV images and the interrogation results are discussed.