Papers by Keyword: Cellular Automata (CA)

Abstract: In this paper, the evacuation strategies and the update rules for limited visibility are proposed. The formulas on single exit, double exits and four exits for low pedestrian density are deduced and showed; and the time ratio is 1: 0.71: 0.56. The simulation results show that for normal visibility, the exit should be designed in the middle of wall, which results in the shortest evacuation time. So each exit is designed in the middle of wall. Moreover, in the different exit cases the evacuation can be simulated very well using the proposed model; and the time ratio on single exit, double exits and four exits is 1: 0.68: 0.57,which is close to the theory value 1: 0.71: 0.56. More, the evacuation evolution of different pedestrian number is studied; and the results show that if no jamming, the time ratios of different pedestrian number accord with the theory value 1: 0.71: 0.56 mainly, which proves the correctness of evacuation model and theory analysis.

Abstract: A improved dynamic parameters model is presented based on cellular automata in this paper.The dynamic parameters: Direction-parameter, Empty-parameter and Cognition-parameter are formulated to simplify tactically the decision-making process of pedestrians, which can reflect the pedestrian judgment on the surrounding conditions and decide the pedestrians choice of action. Simulation of pedestrian evacuation and pedestrian moving rules were established, according to two-dimensional cellular automaton Moore neighborhood. In the improved model, the impact of the pedestrian density around exits is considered, the simulation and experimental results prove that this improvement makes sense, because besides the spatial distance to exits, people may also choose the exit according to the pedestrian density around exits. And the simulation results of improved model is compared with experiment, comparison shows that the improved model can reproduce the experiment well. The improved model is useful for further study, it is instructional significant for pedestrian evacuation, avoiding or reducing the number injuries.

Abstract: Based on the cellular automata (CAs) method of Moore neighbor type, a model of simulation for grain growth processes in magnesium alloy heat affected zone of laser melt injection was established. The results show that the grain growth process can be simulated very well by the CAs method, the shapes of grains tend to be hexagonal, the small grain is annexed by large grains, the grain growth index can be obtained as 0.42, and the topological feature reflected by the established model is accord with the physical mechanism of the grain growth. The cellular automaton (CA) method is proved to be a simple and effective approach for the grain growth simulation.

Abstract: In order to effectively reduce evacuation time of pedestrians in emergencies, a novel evacuation model is proposed based on the three-dimensional cellular automation. The model, according to Moore cellular structure, firstly defines location income and estimates evacuation time parameter, and then gives calculation formula for moving probability of pedestrians at next moment. Meanwhile, in combination with the degree of fear and moving speed, evacuation strategies and cellular evolution rules suited to the three-dimensional condition are raised. At last, by establishing simulation model, the article profoundly analyses key factors that affect evacuation time of pedestrians, and finds that the evacuation time shows a negative correlation with the exit width, but a positive correlation with pedestrian density. Appropriate increase of pedestrians fear degree is good for reducing the whole evacuation time.

Abstract: In emergencies such as fire, pedestrian evacuation for bad visibility is significantly different to the evacuation for normal visibility. In the novel evacuation model, the strategies of pedestrian evacuation and the moving rules are proposed. Then the formulas of the evacuation time are achieved and the time ratio is 0.63. More, using the programming language, pedestrian evacuation is simulated and reproduced. The studies shows that the proposed evacuation model can well reflect the process of pedestrian evacuation; and the evacuation signs of reasonable design can significantly optimize the process. The calculation results also show that the ratio of evacuation time between considering evacuation signs and no evacuation signs is close to 0.63 that is the theoretical results.

Abstract: The CA-based Model of unidirectional pedestrian flow simulation is established. Model takes into account pedestrian forward, change lanes , side forward, backward , away from the dense crowd behavior. Simulation research and analyzed the relationship between pedestrian flow speed ,flow speed, flow , without moving the proportion of pedestrians and the pedestrian density in different pedestrian density. The results showed that: unidirectional pedestrian flow with the pedestrian density increases, there will be two thresholds K₁ and K₂. Pedestrian flow velocity will appear slight and obvious decrease after these two thresholds. Pedestrian flow traffic reaches its maximum value at K_2. The proportion of unmoving pedestrians will increase and the increased amplitude increases when it reaches at the two thresholds K₁ and K₂.

Abstract: The material properties are strongly depended on the microstructure. Recently, for modeling and prediction of microstructure evolution during the forming processes a cellular automata method is used. Combination of several methods in multiscale model allows to extend the possibilities of each method and obtain more reliable results, which are close to the real conditions. The objective of this study is development of multiscale model of microstructure evolution during the shape rolling process and use it for simulation of rolling of 5 mm round bars. Model uses for calculations the finite element (FEM) and cellular automata (CA) methods. Modeling consists of three stages: design of the shape rolling schedule with the definition of shape and sizes of grooves (FEM simulation of each pass, starting from the last pass), FEM modeling of shape rolling in the proper sequence of the passes, modeling of microstructure evolution by frontal cellular automata (FCA). Stages (especially the last two) can be repeated several times to optimize the technology in view of final microstructure. The paper presents the first stage of modeling, which includes design and selection of grooves scheme with used the finite element method. The last six passes were modeled. The rolling scheme obtained from the modeling in the next stage is simulated by FEM to obtain thermomechanical parameters of the process. Then, temperature, strain and strain rate distributions in bar cross-sections, rolling time and inter-pass time will be used as input data for modeling by FCA.

Abstract: In order to fill the blank of the conventional bus routes and to provide a door-to-door transportation service, community bus is a new mode to connect the last mile of public transportation. This paper built a cellular automata model of opening boundary conditions based on the community bus route to explore that the running rules of community bus. Through numerical simulations using departure time interval and passenger arrival rate as index, phase diagrams are obtained and characteristics are found.

Abstract: Carbon deposition forming a nanolayer on a light alloy substrate is a physico-chemical process of the discrete type in all of its aspects. Thus, use of cellular automata, intrinsic discrete, as a mathematical tool for modelling, is fully justified. We adopted two-dimensional (i.e. surface), two-layer automation with Moore vicinity of a cell, for modelling of the carbon deposition process, starting from bonding to the light alloy substrate, leading through layer growth and finishing at the phase transition process, converting graphite into diamond form. To achieve this, we related the transition probabilities of the automaton with the Lennard-Jones potentials for carbon and metal atoms, as well as the physico-chemical conditions in the reaction environment gaseous hydrocarbons density and their particles energy distribution (Maxwell). Taking it into account allowed us to establish an automation time scale of about 1s per calculations run, which has resulted in a simulated layer thickness growth rate well matched with observed results. Using of the two-layer automation allowed us to make some survey into the mechanism of the graphite/diamond transition in the real environmental conditions we met. This demanded further thorough investigations to properly model the spatial structure of mutually interleaved areas of the graphite and diamond type carbon, giving not only a flat-surface but also a vertical structure. The overall surface morphology of the simulated nanolayer we have compared with those of AFM survey performed on real samples, observing relatively good matching in terms of statistical parameters of the surface.

Abstract: An improved cellular automata model is proposed to study the pedestrian counter flow in corridors with different placements of barriers. The model considers the sensing region, collision avoidance, following, position exchange, and other common pedestrian behaviors. The sensing region here considers not only the number of pedestrians, but also their distances, velocities, both of which affect pedestrians’ transition probabilities. For example, when confronting with opposite pedestrians in high speed, the pedestrian may prefer to slow down or change the original direction. In the model, the pedestrians can change their velocities according to different situations. Simulations are conducted with the proposed model and the effect of different placements of barriers in corridors is studied in detail. The flow rates in different situations are compared, and it is found that certain placements of barriers can obviously improve the corridor’s pedestrian capacity, which may contribute to corridor design in the future.