一种3D仿真机房模型分析

本文讨论一种合理的绿色机房模型,求出了在不同的任务量、分配方式、空调风速和空调温度下机房的平均温度、热点、以及热分布和气流速度分布图。分别用人工神经网络和模拟仿真软件Airpak 软件建立模型分析空调的热分布。通过在Airpak中更改机柜发热功率、空调的送风温度、送风速度来模拟仿真不同情况下机房的热循环过程。最后进行改进和优化,使其能够适应更多情况和条件。     

UNSTEADY STATE DISPERSION OF AIR POLLUTANTS UNDER THE EFFECTS OF DELAYED AND NONDELAYED REMOVAL MECHANISMS

Abstract In this paper, we present a two‐dimensional time‐dependent mathematical model for studying the unsteady state dispersion of air pollutants emitted from an elevated line source in the atmosphere under the simultaneous effects of delayed (slow) and nondelayed (instantaneous) removal mechanisms. The wind speed and coefficient of diffusion are taken as functions of the vertical height above the ground. The deposition of pollutants on the absorptive ground and leakage into the atmosphere at the inversion layer are also included in the model by applying appropriate boundary conditions. The model is solved numerically by the fractional step method. The Lagrangian approach is used to solve the advection part, whereas the Eulerian finite difference scheme is applied to solve the part with the diffusion and removal processes. The solutions are analyzed to observe the effects of coexisting delayed and nondelayed removal mechanisms on overall dispersion. Comparison of delayed and nondelayed removal processes of equal capacity shows that the latter (nondelayed) process is more effective than the former (delayed removal) in the removal of pollutants from the atmosphere.     

Effect of pollutant source location on air pollutant dispersion around a high-rise building

This article investigates the dispersion of airborne pollutants emitted from different locations near a high-rise building. A Computational Fluid Dynamics (CFD) model for simulating the wind flow field and the pollutant dispersion was developed and validated by wind tunnel data. Then the spreading of the pollutant emitted from different locations to a rectangular-shaped high-rise residential (HRR) building was numerically studied. The pollutant source location was set in a wide range of the position angle and distance between the source and the building. It was found that the pollutant concentration on the building decreases with an increase in the emission distance whereas the effect of the position angle is more complicated. Interestingly, there is a critical range of the position angle from which the emitted pollutants will not spread to the building in a significant way. The effect of the source location was linked to the wind flow field around the building, particularly with several major flows. The vertical distributions of the pollutant concentration on different faces were also investigated, and it was found that these are more affected by the vertical flow near each face. Finally, a mathematical model was developed to evaluate the pollutant concentration as a function of the emission distance and position angle. These findings are helpful to the understanding of the dispersion of airborne pollutants around high-rise buildings and the related hazard management in urban design.     

A dynamic evaluation framework for ambient air pollution monitoring

Accurate real-time prediction of urban air quality is one of the most important problems in control and improve ambient air condition globally. Therefore, the modeling and applications of air pollutant forecasting and evaluation has attracted the attention of researchers in recent years. Based on the method of fuzzy mathematical synthetic evaluation, this paper built a dynamic evaluation model for the purpose of mastering the future air quality immediately. A newly proposed computational intelligence optimization algorithm is improved to optimize the least square support vector machine, which can generate rolling forecasts of six air pollutants concentration. The information of future air quality status is built by the fuzzy synthetic assessment model based on entropy weighing method. The results and analysis of air quality monitoring show that accurate and reliable forecast of urban air pollutants concentration are possible and the air quality conditions can be evaluated objectively. Through the simulation design, it proves that the proposed dynamic evaluation model can provide a practical tool for ambient air ambient quality evaluation.     

A METAPOPULATION MODEL WITH DISCRETE SIZE STRUCTURE

ABSTRACT. We consider a discrete size‐structured meta‐population model with the proportions of patches occupied by n individuals as dependent variables. Adults are territorial and stay on a certain patch. The juveniles may emigrate to enter a dispersers' pool from which they can settle on another patch and become adults. Absence of colonization and absence of emigration lead to extinction of the metapopula‐tion. We define the basic reproduction number R₀ of the metapopulation as a measure for its strength of persistence. The metapopulation is uniformly weakly persistent if R₀> 1. We identify subcritical bifurcation of persistence equilibria from the extinction equilibrium as a source of multiple persistence equilibria: it occurs, e.g., when the immigration rate, into occupied patches, exceeds the colonization rate (of empty patches). We determine that the persistence‐optimal dispersal strategy which maximizes the basic reproduction number is of bang‐bang type: If the number of adults on a patch is below carrying capacity all the juveniles should stay, if it is above the carrying capacity all the juveniles should leave.     

HABITAT PATCH OCCUPANCY DYNAMICS OF GLAUCOUS‐WINGED GULLS (LARUS GLAUCESCENS) II: A CONTINUOUS‐TIME MODEL

ABSTRACT. The diurnal distribution and abundance dynamics of loafing Glaucous‐winged Gulls (Larus glaucescens) were examined at Protection Island National Wildlife Refuge, Strait of Juan de Fuca, Washington. Asynchronous movement of gulls among three habitat patches dedicated to loafing was modeled as a function of environmental variables using differential equations. Multiple time scale analysis led to the derivation of algebraic models for habitat patch occupancy dynamics. The models were parameterized with hourly census data collected from each habitat patch, and the resulting model predictions were compared with observed census data. A four‐compartment model explained 41% of the variability in the data. Models that predict the dynamics of organism distribution and abundance enhance understanding of the temporal and spatial organization of ecological systems, as well as the decision‐making process in natural resource management.     

A new ray tracing heat source model for mesoscale CFD simulation of selective laser melting (SLM)

The present work was aimed to develop a new ray tracing heat source model used in mesoscale finite volume method (FVM) simulations for the selective laser melting (SLM) process. By means of the metal-gas interface built via the volume of fluid (VOF) method, the developed model simulated the interactions between the laser beam and the powder bed. Multiple reflections of the laser beam at the surface of the metal powders were taken into account in the modeling. Integrated into the commercial software, FLOW3D, the heat source model was validated by the comparison between the calculation results and previous experiments. 3-D mesoscale simulations for the SLM process of 316 L stainless steel were performed. The result indicated that the proposed ray tracing heat source model was able to model the laser heating process of the SLM. Better than the conventional one, the new heat source model identified the local defects during the SLM process, such as the balling behavior.     

Unsteady state mathematical model of chemically reactive pollutants from an instantaneous line source into a stable atmospheric boundary layer

A time dependent atmospheric model represented for chemically reactive primary pollutants emitted from an elevated line source into a stable atmospheric boundary layer over a surface terrain. The model obtained from an analytical solution of the atmospheric diffusion equation with the quadratic diffusion coefficient (exchange coefficient) and the variable wind velocity taken to be of three different types’ viz. constant, constant shear and parabolic functions of vertical height. The pollutants considered to be of chemically reactive primary pollutants emitted from a time-dependent line source of Instantaneous type. In order to facilitate the application of the model the results for the general situation that includes chemical reaction rate & time dependent source incorporated in the model.     

Modeling the removal of gaseous pollutants and particulate matters from the atmosphere of a city

In this paper, a nonlinear mathematical model is proposed and analyzed to study the removal of gaseous pollutants and particulate matters from the atmosphere of a city by precipitation. The atmosphere consists of four interacting phases i.e. the raindrops phase, the gaseous pollutants phase, the phase of gaseous pollutants absorbed (dissolved) in rain drops and the phase of particulate matters. The dynamics of these phases is assumed to be governed by ordinary differential equations with source, interaction, removal and recycle terms. The proposed model is analyzed by using stability theory of differential equations. It is shown that the pollutants can be removed from the atmosphere and their removal rates depend mainly upon the rates of emission of the pollutants, rate of rain drops formation and the rate of falling rain drops on the ground. If the rate of precipitation is very high, the pollutants may be removed completely from the atmosphere.     

Dusty Supersonic Flow Past a Blunt Body: Viscous and Nonstationary Effects

High‐speed space‐ or aircrafts travelling through a dusty atmosphere may meet dust clouds in which the particles are often distributed very nonuniformly. Such nonuniformities may result in the onset of unsteady effects in the shock and boundary layer and (that is of prime interest) unsteady heat fluxes at the stagnation region of the vehicle. In the nearwall region of high‐speed dusty‐gas flow, there may take place regimes with and without particle inertial deposition, which require essentially different mathematical models for describing the heat transfer [1]. The present paper deals with two problems, considered within the framework of the two‐fluid model of dusty gas [2]: (i) determination of the limits of the particle inertial deposition regime and the distribution of dispersed‐phase parameters near the frontal surface of a sphere immersed in dusty supersonic flow (Mach number M = 6) at moderate flow Reynolds numbers (10² ≤ Re ≤ ∞); (ii) effect of free‐stream nonuniformities in the concentration of low inertial (non‐depositing) particles on the friction and heat transfer at the stagnation point of the body at high Re and M.     

Parasitism and host patch selection: A model using aggregation methods

There is a growing interest in studying the effects of parasites on the modification and evolution of hosts' behaviour. In this paper, we deal with a case of parasitism affecting the spatial pattern of host distribution. We develop a simple model with two patches, one host and one parasite. Parasites live in Patch 1, hosts live in the two patches and migrate from one patch to the other. We study the case of a migration independent of parasite density and the case of a migration dependent on density. In the two cases, we make the assumption that the choice of patch is fast, whereas the growth of populations are slow. So we use aggregation methods which are particularly adapted for systems exhibiting different times scales. The aggregated model obtained in the case of a density independent migration is a classical predator-prey model. The case of a density dependent migration aggregated model is very different and a nonstandard one, and exhibits an interesting result. Under certain conditions, parasites always become extinct in the case of a density independent migration, whereas the adaptation of hosts (density dependent migration) allows to stabilize the host-parasite system.This first application of the aggregation methods to epidemiology is very promising because these methods allow us to deal with more real assumptions about the behavioural interplay between hosts and parasites.     

INCORPORATION AND INFLUENCE OF VARIABILITY IN AN AGGREGATED FOREST MODEL

ABSTRACT. Variability influences ecological processes at various scales and is incorporated in different ways in forest models. The forest model Dis CFor M scales an individual based, stochastic forest patch model up to a height structured tree population model. To describe the variability arising from stochastic processes in the patch model, Dis CFor M uses theoretical random dispersions of trees in each height class over all patches. This yields a spatial distribution of light and consequently of light dependent process rates. Three major influences of variability on simulations are examined: site condition, patch to patch, and temporal environmental variability. Simulation studies and comparison with forest compositions from the Swiss National Forest Inventory reveal that these influences affect simulated forest dynamics, species composition, and biodiversity, depending on climatic boundary conditions and hence have to be taken into account in modeling.     

Numerical simulation of pollutant dispersion in street canyons: Geometric and thermal effects

Numerical investigations on pollutant dispersion in street canyons with emission sources located near the ground level are performed in the present work. Pollutant dispersion problems in urban areas are usually studied considering the street canyon model, which consists of long streets laterally confined by buildings. Significant changes can be observed in wind flow patterns and pollutant concentration fields when thermal and geometric effects are considered. Thus, the objective of this study is to investigate numerically the wind flow and pollutant dispersion for the following cases: (a) a two-dimensional street canyon model considering three different aspect ratios and four different wall heating configurations; (b) a flow domain with two immersed buildings arranged in two distinct configurations; (c) a three-dimensional urban area model composed of a building set and street intersections. Expected flow structures were obtained inside the canyon when different aspect ratios and wall heating configurations were considered. Flow phenomena such as separation/reattachment were observed when two-buildings models were analyzed. Finally, three-dimensional flow structures, with some characteristic that are not observed in two-dimensional models, affecting the pollutant removal, were simulated in the last case, highlighting the relevance of model dimensionality. The wind flow and pollutant dispersion are investigated using a numerical model based on the finite element formulation utilized by some of the authors of this work, which is extended here to deal with problems of heat and mass transport in the urban micro-scale. Turbulence is reproduced using Large Eddy Simulation (LES) and thermal effects on the momentum equations are considered as a buoyancy force, according to Boussinesq approximation.     

Dynamics analysis of a quarantine model in two patches

A new deterministic model for assessing the impact of quarantine on the transmission dynamics of a communicable disease in a two‐patch community is designed. Rigorous analysis of the model shows that the imperfect nature of quarantine (in the two patches) could induce the phenomenon of backward bifurcation when the associated reproduction number of the model is less than unity. For the case when quarantined susceptible individuals do not acquire infection during quarantine, the disease‐free equilibrium of the model is shown to be globally asymptotically stable when the associated reproduction number is less than unity. Furthermore, the model has a unique Patch i‐only boundary equilibrium (i = 1,2) whenever the associated reproduction number for Patch i is greater than unity. The unique Patch i‐only boundary equilibrium is locally asymptotically stable whenever the invasion reproduction number of Patch 3 ? i is less than unity (and the associated reproduction number for Patch i exceeds unity). The model has at least one endemic equilibrium when its reproduction number exceeds unity (and the disease persists in both patches in this case). It is shown that adding multi‐patch dynamics to a single‐patch quarantine model (which allow the quarantine of susceptible individuals) in a single patch does not alter its quantitative dynamics (with respect to the existence and asymptotic stability of its associated equilibria as well as its backward bifurcation property). Copyright © 2014 John Wiley & Sons, Ltd.     

Lagrangian particle dispersion simulations in cases of sea-breeze convergence

The impact of sea-breeze convergence on air quality in an area of complex coastlines and orography in northern New Zealand is investigated. Results of simulations using a mesoscale model and a Lagrangian particle dispersion model for an idealised case are described. These show that the convergence zones limit the exchange of air between opposing circulations while providing a means of elevating near-surface pollution. This provides a mechanism for transport of relatively polluted air many kilometers from the original source with potential for re-mixing to the surface the following day.     

Improvement of source and wind field input of atmospheric dispersion model by assimilation of concentration measurements: Method and applications in idealized settings

The problem of correcting the pollutant source emission rate and the wind velocity field inputs in a puff atmospheric dispersion model by data assimilation of concentration measurements has been considered. Variational approach to data assimilation has been used, in which the specified cost function is minimized with respect to source strength and/or wind field. The analyzed wind field satisfied the constraints derived from the conditions of mass conservation and linearized flow equations for perturbations from the first guess wind field. ‘Identical twin’ numerical experiments have been performed for the validation of the method. The first guess estimation errors of source emission rate and wind field were set to a factor of up to 10 and up to 6 m/s respectively. The calculations results showed that in most studied cases an improvement of vector wind difference (VWD) error by about 0.7–1 m/s could be achieved. The resulting normalized mean square error (NMSE) of concentration field was also reduced significantly.     

哈尔滨市冬季PM_(2.5)与影响要素的相关分析

运用相关性分析方法,研究哈尔滨市PM_(2.5)质量浓度与主要空气污染物及气象因素之间的相关关系.建立PM_(2.5)与影响其质量浓度变化的因素的单因变量的偏最小二乘回归分析(PLS1)模型,模型拟合良好,由模型知CO是导致PM_(2.5)质量浓度升高的主要因素.运用通径分析方法,研究解释变量对因变量的直接影响、通过其他解释变量对因变量的间接影响以及各解释变量的对因变量的协同作用.结果表明,各解释变量对PM_(2.5)质量浓度变化的总作用从大到小依次为:CO、PM_(10)、NO_2、风速、湿度、SO_2.     

Permanence of dispersal population model with time delays

Permanence of a dispersal single-species population model is considered where environment is partitioned into several patches and the species requires some time to disperse between the patches. The model is described by delay differential equations. The existence of food-rich patches and small dispersions among the patches are proved to be sufficient to ensure partial permanence of the model. It is also shown that partial permanence ensures permanence if each food-poor patch is connected to at least one food-rich patch and if each pair in food-rich patches is connected. Furthermore, it is proved that partial persistence is ensured even under large dispersion among food-rich patches if the dispersion time is relatively small.     

基于DMC方法的城市空气质量SUR模型研究

我国现阶段城市化的日益发展,使城市空气质量的宏观调控面临越来越大的压力。本文建立了关于空气质量的似乎不相关(SUR)模型,采用Jeffreys's的不变先验分析直接蒙特卡罗(DMC)方法,计算各参数的贝叶斯后验密度和未来值的预测密度。对中国厦门市区三项污染指标及四项外部驱动因素的数据进行实证分析,并将其与贝叶斯分层模型得出的结果进行比较。