Simulation-based approach to design of inherently safer processes

Safety of chemical processes and plants is a matter of high priority. The design of an inherently safer process is one of very beneficial ways of achieving this goal.The paper describes the method of designing an inherently safer process for a chosen set of equipment and materials involved by applying non-linear optimization. The optimization is aimed at finding an operational mode, which guarantees safety of the process under normal conditions and provides maximal attainable safety in case of one typical accident scenario – cooling failure. Discussion covers problem statement, choice of the optimization criteria, appropriate methods for defining control variables.An important practical challenge is stability analysis of the optimized process mode with respect to permissible deviations of control parameters and variables from the estimated values. The original method for the stability analysis of a non-stationary process is proposed. It comprises simplified preliminary evaluation method followed by the more detailed numerical optimization-based analysis.Several examples illustrate application of the methods proposed.     

地铁车厢汽油火灾的模拟计算与分析

采用数值计算方法,研讨了泼洒燃料总量为5kg汽油的故意纵火情况下产生的火灾功率、烟气的蔓延规律及烟气控制方案。首先理论分析了泼洒液体火灾的液面深度、浸铺面积、单位面积燃料质量损失速率,进而得到了泼洒液体燃料总量与火灾功率的关系。采用多分区区域模型对列车车厢内的烟气温度、厚度进行了计算。分析车厢5kg汽油火灾的烟气危险性中,发现烟气将在30s时下降到危险高度,烟气温度将在30~50s后超过人体的极限,90s后烟气降到车厢地板,150s后车厢会达到轰燃温度。基于数值模拟结果,笔者提出了烟气控制方案。研究成果有助于地铁防灾设计及人员疏散紧急预案的制定。     

大空间建筑烟气填充研究方法的对比

为了对大空间建筑烟气填充研究方法进行对比分析。以一个废弃的大空间仓库为研究对象,采用了全尺寸火灾实验、计算机数值模拟和理论分析相互应用验证的研究方法,研究理论及数值模拟两种火灾烟气层高度的描述方法的准确性。结果表明当采用t2火模型时,在与现实的吻合程度方面,数值模拟〉Zukoski理论模型〉Yamana-Tanaka理论模型;随着火灾的不断发展,相对误差逐渐增大。通过对比分析发现,全尺寸实验、理论模型和数值模拟三种方法相互验证可以更好地保证研究的准确性;总结得到了两种与现实较吻合的描述烟气层高度的理论方法,并且提出减小误差应注意的几点事项,包括尽可能提高火源热释放速率、烟气层温度描述的准确性;不考虑火源热量通过建筑边界结构散失等。     

数值模拟在我国火灾研究中的应用

为了解数值模拟方法在我国火灾研究中的应用情况,从CNKI《中国学术期刊(网络版)》数据库中获取1265篇以火灾数值模拟为主题的期刊文献,使用CiteSpace可视化分析软件,从机构合作、作者合作、关键词共现等方面进行分析。结果表明:2003年以来,火灾数值模拟高速发展,应用广泛,并不断被用以研究新的火灾问题。中国科学技术大学火灾科学国家重点实验室是使用数值模拟方法研究火灾最主要的科研机构;朱国庆、周汝等是发表火灾数值模拟相关文献最多的学者;火灾数值模拟主要应用于大体量火灾场景,也用于获取实体实验难以监测的数据,使用最广泛的火灾数值模拟软件为FDS。     

Estimating surface acoustic impedance with the inverse method

Sound field parameters are predicted with numerical methods in sound control systems, in acoustic designs of building and in sound field simulations. Those methods define the acoustic properties of surfaces, such as sound absorption coefficients or acoustic impedance, to determine boundary conditions. Several in situ measurement techniques were developed; one of them uses 2 microphones to measure direct and reflected sound over a planar test surface. Another approach is used in the inverse boundary elements method, in which estimating acoustic impedance of a surface is expressed as an inverse boundary problem. The boundary values can be found from multipoint sound pressure measurements in the interior of a room. This method can be applied to arbitrarily-shaped surfaces. This investigation is part of a research programme on using inverse methods in industrial room acoustics.     

Numerical simulation of hydrogen–air detonation for damage assessment in realistic accident scenarios

An accidental hydrogen release within an equipment enclosure may result in the presence of detonable mixture in a confined environment. From a safety standpoint, it is then useful to assess the potential for damage. In that context, numerical simulation of the sequence of events subsequent to detonative ignition provides a useful tool, although with obvious limitations. This article describes the procedure, summarizes two case studies, and reviews the limitations. First, a hydrogen dispersion pattern is obtained from numerical simulation of dispersion, using a commercial package designed primarily for incompressible flow. This dispersion cloud is then used as the initial condition in an inviscid, compressible, reactive flow simulation. To force detonative ignition, a sufficiently large amount of energy is deposited in a small region that corresponds to the ignition location. Chemistry is modeled using a single step Arrhenius model. Because the wave thickness is small compared with the computational domain, a fine mesh is needed, limiting the practicality of the process to two-dimensional geometries. This is the most significant limitation; it is conservative. The two cases described in the paper include an electrolyzer, in which a small release occurs, leading potentially to some damage to the enclosure, and a reformer, in which the consequences are potentially more serious.     

Combustion modeling in large scale volumes using EUROPLEXUS code

Most of the numerical benchmarks on combustion in large scale volumes for hydrogen safety, which were performed up until today have demonstrated, that current numerical codes and physical models experience poor predictive capabilities at the industrial scale, both due to under-resolution and deficiencies in combustion modeling. This paper describes a validation of the EUROPLEXUS code against several large scale experimental data sets in order to improve its hydrogen combustion modeling capabilities in industrial settings (e.g. reactor buildings). The code is based on the Euler equations and employs an algorithm for the propagation of reactive interfaces, RDEM, which includes a combustion wave, as an integrable part of the Reactive Riemann problem, propagating with a fundamental flame speed (being a function of initial mixture properties as well as gas dynamics parameters). Validation of the first combustion model implemented in the code is based on obstacle-laden channels, interconnected reactor-type compartments, vented enclosures and covers all major premixed flame combustion regimes (slow, fast and detonation) with an aim to obtain conservative results. An improvement of this model is found in a direction of transient interaction of flame fronts with regions of elevated integral length scales presented in the velocity gradient field due to e.g. interactions with geometrical non-uniformities and pressure waves.     

尾矿库重金属污染物迁移的现代数值模拟方法

为了给研究重金属污染物迁移提供指导性的方法和步骤,力求总结出尾矿库重金属污染物迁移的一般性研究方法。以尾矿库重金属污染为研究对象,采用事故树和鱼刺图对尾矿库重金属污染进行分析,找出主要污染源,建立污染物迁移数学模型,系统地归纳尾矿库重金属污染物迁移数值模拟软件,对主要污染源进行分析得出结论。结果表明各种研究手段之间存在步步深入,前后承接的联系,由此建立尾矿库重金属污染物迁移的现代数值模拟方法,提出尾矿库重金属污染物迁移的数值模拟方法的一般操作步骤。     

采空区对地表建筑物的影响评价方法研究

为研究金属矿山采动灾害影响,论述了金属矿山采空区上覆岩层移动对地表建筑物影响评价理论和技术方法,即"三带理论"、岩石移动带理论和数值模拟方法;指出了金属矿山空区稳定性和岩石移动的主要影响因素。结合某铁矿采空区的实际情况,综合应用这3种方法对该铁矿进行了定性、定量评价。分析3种评价方法的特点,旨在探索金属矿山的采动影响评价方法,以便保护矿区附近建筑物的安全,减小采动灾害对矿山企业及附近居民生命财产损失。     

Potential of a Precrash Lateral Occupant Movement in Side Collisions of (Electric) Minicars

Objective: In minicars, the survival space between the side structure and occupant is smaller than in conventional cars. This is an issue in side collisions. Therefore, in this article a solution is studied in which a lateral seat movement is imposed in the precrash phase. It generates a pre-acceleration and an initial velocity of the occupant, thus reducing the loads due to the side impact.

Methods: The assessment of the potential is done by numerical simulations and a full-vehicle crash test. The optimal parameters of the restraint system including the precrash movement, time-to-fire of head and side airbag, etc., are found using metamodel-based optimization methods by minimizing occupant loads according to European New Car Assessment Programme (Euro NCAP).

Results: The metamodel-based optimization approach is able to tune the restraint system parameters. The numerical simulations show a significant averaged reduction of 22.3% in occupant loads.

Conclusion: The results show that the lateral precrash occupant movement offers better occupant protection in side collisions.     

GIS与数模支持下的油气田环境风险预警系统研究

简要介绍了油气田在建设与生产过程中对环境的影响,构建并开发了基于GIS与数模的油气田环境风险预警系统。系统包含大气污染模拟模型、地表水污染模拟模型和地下水污染模拟模型,实现了环境监测数据的管理、实时监测预警和污染模拟、快速应急响应三大功能。介绍了油气田环境风险预警系统的设计及基本功能,探索了将地理信息系统与数学模型相结合运用于油气田环境风险预警的方法。实践表明,以GIS技术为平台,结合数学模型为辅助进行环境风险预警是可行的。     

A numerical study of the evolution of the blast wave shape in rectangular tunnels

When the explosion of condensed materials occurs in square or circular cross-section tunnel, the subsequent blast wave reveals two patterns: three-dimensional close to the explosive charge and one-dimensional far from the explosion. Pressure decays for these two patterns have been thoroughly studied. However, when the explosion occurs in rectangular cross-section tunnel, which is the most regular geometry for underground networks, the blast wave exhibits a third, two-dimensional, patterns. In order to assess the range of these three patterns, several numerical simulation of blast waves were carried out varying the width and the height of the rectangular cross-section as well as the mass of the charge. Laws are presented to localize the transition zones between the 3D and the 2D patterns, and between the 2D and the 1D patterns, as functions of non-dimensional width and height. The numerical results of the overpressure are compared to existing 3D and 1D laws. An overpressure decay law is proposed to represent the 2D pattern. Knowing the two transition zones and the overpressure decays within these zones, an algorithm is presented to efficiently predict an overpressure map. This algorithm is validated by comparison with experimental data.     

Numerical and reduced-scale experimental investigation of blast wave shape in underground transportation infrastructure

When an explosion occurs in a tunnel, the study of the blast wave quickly becomes complicated, owing to the multiple propagation patterns of the blast wave (incident wave, regular and Mach reflections) and to the geometrical conditions. Considering this problem, two patterns can be revealed. Near the explosive, the well-known free-field pressure wave can be observed. After multiple reflections on the tunnel's walls, this overpressure behaves like a one-dimensional (1D) wave. One aim of this paper is to determine the position of this transition spherical-to-planar wave propagation in a tunnel using both numerical and reduced-scale experiments, and thereby validate the dedicated law established in a previous work.For this purpose, a detonation of TNT in a tunnel with a cross-section of up to 55 m² is considered. Results show good agreement between the numerical simulations and experiments. The transition zone between the three-dimensional (3D) and the 1D wave is well detected. An application to a simplified subway station is also investigated which shows that significant planar waves can be transmitted to the neighboring stations via the junction tunnels.     

Numerical simulation of far-field blast loads arising from large TNT equivalent explosives

Large TNT equivalent explosions usually arise from accidents occurring during the transportation, storage, and manufacturing of chemicals relevant to process industries. The blast wave generated by the explosion will spread and interact with the surrounding factories and storehouses, damaging the building structures within several kilometers and causing significant casualties and property losses. This study aims to develop an efficient numerical simulation method to predict blast loads to estimate the consequences of accidents involving far-field free air bursts or surface burst explosions. Before its interaction with the interested target, a blast wave is generated in the numerical model by specifying the initial and boundary conditions of the disturbed air. Based on empirical data of incident overpressure, an explicit formula to calculate the air particle velocity is derived from the governing equations of a perfect inviscid gas. A simplified path line method is proposed to calculate the air density. The proposed method is applied to the LS-DYNA CESE solver to simulate the blast loads on building structures in the far field. Validations against empirical data and experiments indicate that the proposed method is sufficiently accurate for engineering applications and, through a case study, presents a more efficient performance than the LOAD_BLAST_ENHANCED (LBE) and mapping methods.     

Modelling bund overtopping using a shallow water CFD model

This paper describes the development of a model for assessing the hazards arising from liquid spills from storage tanks containing flammable liquids. The model is based on computational fluid dynamics (CFD) solutions to the shallow water equations and is able to account for the interaction of a liquid spill with sloping ground and walls/bunds. These features mean that it has a much wider range of applicability than simple models and yet, as it is based on the solution to the two-dimensional shallow water equations, is relatively quick to run. The key parameter of interest in risk assessments is the fraction of a tank contents that would overtop the surrounding wall/bund that has been designed to retain it. A simple ‘sub-model’ has been developed to take account of this three-dimensional phenomenon within the two-dimensional model. The numerical solution of the shallow water equations is obtained through an adaptive method using two shock-capturing numerical techniques; the weighted average flux (WAF) and random choice methods (RCM). These provide a robust solution algorithm. A simple test case has been used to demonstrate the applicability of the model.     

煤层条带开采整体安全系数确定方法研究

为评价工程中条带开采方案的煤层整体稳定性,确定开采方案的安全程度,基于强度折减原理,应用FLAC3D数值模拟软件,将工程实际与数值实验相结合,研究煤层条带开采对地表沉陷、围岩变形和破坏的影响,用安全系数对安全程度进行评价。提出条带开采整体失稳的临界状态判断标准为采空区之间及采空区至地表岩体塑性区域连通,并以地表最大沉降和顶板最大位移突然增大作为临界状态判断标准的验证条件,结果表明:应用强度折减原理进行数值模拟确定的条带开采整体安全系数与工程实际相吻合。     

泄爆容器中粉尘爆炸的试验研究与数值模拟

为了解泄爆容器中粉尘爆炸的发展过程,采用试验和数值模拟相结合的方法对玉米淀粉在圆柱形容器内的泄爆过程进行研究。数值模型采用欧拉–拉格朗日方法模拟粉尘爆炸的两相流问题,通过求解非稳态的湍流两相反应流守恒方程对试验进行二维仿真。试验和模拟结果表明,点火位置对爆炸发展过程有明显影响,点火位置离泄爆口越远,容器中的最大泄爆压力Pred,max越高。在粉尘爆炸的安全防护设计中,应把点火位置作为重要影响因素之一加以考虑。     

HAZOP study training from the 1970s to today

An account is given of HAZOP study training from the simple methods used initially to modern methods such as e-learning courses. An especial mention is given to the role of Trevor Kletz in initiating public courses.     

重气扩散的数值模拟

易燃易爆有毒物质泄漏事故常形成比空气重的气云 ,国外已开发了大量不同复杂程度的重气扩散模型 ,其中数值模拟已成为快速发展的领域。本文综述了重气扩散的湍流模型 ;还描述了数值模拟的计算方法及其准确性 ;最后分析了目前存在的问题 ,提出了今后的发展方向。     

水蒸气抑制甲烷燃烧和爆炸实验研究与数值计算

在爆炸激波管中对水蒸气抑制甲烷燃烧和爆炸进行较系统的实验研究,并对其抑燃、抑爆化学动力学作用机理进行数值计算分析。结果表明:加入一定量的水蒸气后,可以有效降低CH4-O2混合气体的燃烧速度和爆炸强度;当水蒸气量达到某临界值时,CH4-O2混合气体将不能被点燃。化学动力学数值计算结果表明:在混合气体中加入水蒸气后,增大了甲烷的点火延迟时间,降低了燃烧温度和H,O和OH等高活性自由基的浓度。水蒸气能有效抑制甲烷燃烧和爆炸,其作用效果源于其物理抑制和化学阻化的综合效应。