成对行为对行人疏散动力学的影响研究

熟悉的行人之间经常存在着聚集运动的整体跟随行为现象.为了研究这种行为对疏散过程的影响,考虑了行人的并排成对、前后成对、混合成对三种方式,建立了一个新的元胞自动机模型,研究了三种成对方式对双出口房间内行人疏散过程的影响,并分析、讨论了不同参数下成对方式之间的差异. 关键词： 行人流 元胞自动机 成对疏散 计算机模拟     

WALL CONDUCTION EFFECT ON THE ONSET OF THERMAL INSTABILITY IN HORIZONTAL RECTANGULAR CHANNELS

The effect of peripheral thermal conduction in the bottom wall on the onset of thermal instability in the thermal entrance region of horizontal, rectangular, bottom-uniform-heated channels was studied by experiment and theoretical simulation. The predicted results of the onset of thermal instability for the cases of uniform peripheral wall heat flux are in agreement with the published experimental data, but the predicted results for the cases of uniform peripheral wall temperature exceed the previous data by about an order of magnitude. The present experimental data reconfirm the present predictions. The effect of increasing the peripheral wall conduction is shown to stabilize the flow.     

Investigation of Laminar Convective Heat Transfer of a Novel Tio2–Carbon Nanotube Hybrid Water-Based Nanofluid

The current study was conducted to investigate the convective heat transfer coefficient of a novel TiO₂–CNT hybrid nanofluid through the shell-and-tube heat exchanger under a laminar flow and the effects of temperature and mass fraction on it. TiO₂–CNT hybrid nanofluids were prepared using a new and modified hydrolysis technique. The thermal conductivity of the TiO₂–CNT hybrid nanofluid and other thermo-physical properties were assessed. Results indicate that the effective thermal conductivity and heat transfer coefficient of the base fluid was influenced significantly and increased by the 0.2 wt% of this novel hybrid nanofluid in distilled water.     

Large-eddy simulations of temporally accelerating turbulent channel flow

The unsteady turbulent channel flow subject to the temporal acceleration is considered in this study. Large-eddy simulations were performed to study the response of the turbulent flow to the temporal acceleration. The simulations were started with the fully developed turbulent channel flow at an initial Reynolds number of Re₀ = 3500 (based on the channel half-height and the bulk-mean velocity), and then a constant temporal acceleration was applied. During the acceleration, the Reynolds number of the channel flow increased linearly from the initial Reynolds number to the final Reynolds number of Re₁ = 22,600. The effect of grid resolution, domain size, time step size on the simulation results was assessed in a preliminary study using simulations of the accelerating turbulent flow as well as simulations of the steady turbulent channel flow at various Reynolds numbers. Simulation parameters were carefully chosen from the preliminary study to ascertain the accuracy of the simulation. From the accelerating turbulent flow simulations, the delays in the response of various flow properties to the temporal acceleration were measured. The distinctive features of the delays responsible for turbulence production, energy redistribution, and radial propagation were identified. Detailed turbulence statistics including the wall shear stress response during the acceleration were examined. The results reveal the changes in the near-wall structures during the acceleration. A self-sustaining mechanism of turbulence is proposed to explain the response of the turbulent flow to the temporal acceleration. Although the overall flow characteristics are similar between the channel and pipe flows, some differences were observed between the two flows.     

An improved cellular automaton model with the consideration of a multi-point tollbooth

Based on the classical Nagel–Schreckenberg model, we in this paper propose an improved cellular automaton (CA) model to study the influences of a multi-point tollbooth on traffic flow. The numerical results show that the multi-point tollbooth can be looked at as a bottleneck and that it can improve the road capacity compared with other tolling stations, which shows that the proposed model is more effective than other traffic flow models. In addition, the results can help readers to better understand the effects of a multi-point tollbooth on traffic flow and help traffic engineers to reasonably design the tolling station.     

Analysis of Two-Phase Cavitating Flow with Two-Fluid Model Using Integrated Boltzmann Equations

In the present work, both computational and experimental methods are employed to study the two-phase flow occurring in a model pump sump. The two-fluid model of the two-phase flow has been applied to the simulation of the three-dimensional cavitating flow. The governing equations of the two-phase cavitating flow are derived from the kinetic theory based on the Boltzmann equation. The isotropic RNG$k-\epsilon-k_{ca}$ turbulence model of two-phase flows in the form of cavity number instead of the form of cavity phase volume fraction is developed. The RNG $k-\epsilon-k_{ca}$ turbulence model, that is the RNG$k-\epsilon$ turbulence model for the liquid phase combined with the $k_{ca}$model for the cavity phase, is employed to close the governing turbulent equations of the two-phase flow. The computation of the cavitating flow through a model pump sump has been carried out with this model in three-dimensional spaces. The calculated results have been compared with the data of the PIV experiment. Good qualitative agreement has been achieved which exhibits the reliability of the numerical simulation model.     

真空传输线板-锥过渡结构的功率流分析

真空传输线板-锥转角过渡是多模块汇流的Z箍缩装置经常采用的结构,在不考虑磁绝缘失效、介质损耗的前提下,采用有限差分方法分析转角过渡对功率流传输的影响。初步的计算和分析表明:随着转角的变大,由阻抗不匹配引起的反射将使传输效率有所降低;前沿较陡的快脉冲在这种结构中发生严重畸变,而低频脉冲则几乎不受影响。在板-锥过渡设计中采用小转角结构,尽量减小脉冲传输方向的变化,对保证脉冲高效传输有利。     

长光程比色池-流动注射测定水中微量挥发酚

利用长光程比色池 流动注射系统快速测定水样中的微量挥发酚.该方法的检出限为0.232 μg·L^-1,相对标准偏差小于0.553%,相对误差小于0.185%,样品加标回收率在91.0%~99.8%,且标准曲线具有良好线性（r =0.999 9）.与传统国标方法（《水质挥发酚的测定4-氨基安替比林分光光度法》,HJ503-2009）相比,样品浓度测定偏差为2.59%~8.25%,在分析速率上,传统的国标方法约为5个·h^-1,而该方法分析速率达24个·h^-1,能满足大批量样品连续准确测定的要求,特别适合事故性的应急监测.     

基于梯度矢量流和主动轮廓模型的海陆边界提取

利用边缘检测与主动轮廓模型组合的方法可提取海陆边界线,但易受轮廓跟踪的缺点影响.在该方法的基础上,利用边缘检测与梯度矢量流的有向力作用生成初始轮廓线,再使用主动轮廓模型对初始轮廓线进行调整,得到精确的海陆边界.实验证明该方法可简便地生成有效的初始轮廓线并准确提取海陆边界,避免使用轮廓跟踪法.该方法可利用GIS数据辅助以简化提取流程.     

电磁力及其对MIG焊接熔池流场的影响

MIG焊接熔池具有不规则的表面边界,温度较高且分布极不均匀,在电磁力、浮力、表面张力等的作用下发生剧烈运动.基于熔池表面变形较大时电弧电流密度的双峰分布模型,建立了电磁力的计算模型.采用数值模拟技术研究了熔池中的流体力学行为,揭示了焊接工艺参数对熔池流场的影响规律.实验表明,计算与实测结果符合良好.