Stack effects on smoke propagation in subway stations

In fires of subway stations, the most immediate threat to passengers' life is not the direct exposure to fire, but the smoke inhalation because it contains hot air and toxic gases. To understand the mechanisms driving the motion of smoke is therefore an important issue of fire safety, and the stack effect is found to be an important mechanism having significant influence. In this paper, we compute the three-dimensional smoke flow fields under various fires happened in a representative subway station of Taipei Rapid Transit System. To clarify the mechanisms corresponding to the stack effect, a simplified three-dimensional configuration is also considered. Results indicate that, without mechanical smoke control, the stack effect plays a decisive role and is virtually the sole factor influencing the smoke movement. Because of the stack effect, most or sometimes all of the smoke will choose a vertical shaft (usually a stairwell) to evacuate, and the cross sectional area of the shaft and the location of fire determine which shaft is chosen. Present computational results show the evidences of the importance of the stack effect and provide both valuable information to the design of the passenger evacuation routes in fires as well as criteria to the design of smoke control systems of subway stations.Received: 16 January 2003, Accepted: 10 March 2003, Published online: 12 September 2003     

基于光声气体滤波的早期火灾烟气测量方法

火灾烟气中气体和烟雾浓度测量对火灾研究有着重要意义。本文提出一种利用光声技术同时在线测量CO浓度和烟雾消光的非接触式方法。根据气体滤波和粒子散射原理,采用两个光声腔分别作为CO测量腔和烟雾参比腔,在其与光源之间的开放路径中进行火灾产物的测量,通过测量两个光声腔信号,依据信号变化量计算CO浓度和烟雾消光。基于标准火的实验证明该方法可以实现烟雾颗粒和CO气体的复合测量。     

多维地震波作用下地铁车站及场地的地震反应

研究了不同类型多维地震波作用下地铁车站及软土场地的地震反应特征。以上海软土场地条件下的某双层地铁车站为背景,采用有限元方法建立了描述场地土与地铁车站结构相互作用的二维非线性力学模型,其中利用等效线性化方法模拟了土的非线性。以不同类型基岩的多维(含水平向和竖向）地震波作为输入,运用ANSYS软件数值分析了软土场地中地铁车站结构及场地的地震反应,比较了不同类型地震波作用下地铁车站结构和场地地震反应的差异．算例结果表明：在长周期地震波作用下地铁车站结构的内力响应峰值以及场地地表的加速度响应峰值和位移响应峰值均明显大于普通地震波作用下的相应值;考虑竖向地震动时双层地铁车站底层中柱的柱底轴力较单一水平向地震动作用的情形有明显增大;地铁车站的存在使结构上覆土层加速度响应峰值和位移响应峰值有所降低．     

大跨度Y形柱地铁车站结构地震反应研究1）

随着地铁建设的发展,出现了一种新型的结构形式-大跨度Y形柱地铁车站结构,与现有的地铁车站结构完全不同,其空间高大宽敞,环境舒适.为研究该新型地铁车站结构的抗震性能,以北京地铁6号线新华大街站为工程背景,使用FLAC^3D软件建立土与地下结构三维有限差分动力模型,模拟其在新华大街人工波作用下的响应过程,重点分析了车站Y形柱和侧墙的加速度、位移、应变的规律,并与试验结果进行了对比分析,结果表明：数值模拟与振动台试验结果基本一致,体现出了相似的规律性;Y形柱加速度最大位置出现于柱顶端稍下位置,并非于柱顶端;Y形柱分叉位置处应变出现突变,此点相对于柱底的位移最大,且变化率较大,是抗震设计中需要加强的部位;Y形柱加速度、位移变化都会大于侧墙.上述研究成果对提高该类地铁车站结构抗震性能的认识及抗震设计水平提供了合理的参考与指导.     

LIMIT STATE DETERMINATION FOR A SUBWAY STATION STRUCTURE BY INCREMENTAL DYNAMIC ANALYSIS1)

-5 表征地下结构抗震性能的研究不多,而性能化设计方法需要确定结构物在地震作用下的极限状态. 本文根据地铁车站特点,从结构变形性能和止水性能两个方面定义了抗震性能的四个极限状态,并以结构最大层间位移角 作为特征指标. 以上海某多层地铁车站为背景,建立了土--结构二维有限元模型,采用增量动力分析法 研究该类结构的抗震极限状态,建立了增量动力分析法的地震动强度指标结构底部峰值加速度与结构性能指标最大层间位移角 的关系曲线,给出了该地铁车站结构4个极限状态的最大层间位移角界限值.     

土-地铁车站及其上盖结构体系地震反应分析

为研究地震作用下地铁车站及其上盖结构体系的地震反应特征,本文以一典型的地铁车站及上盖结构体系为背景,采用ABAQUS软件建立土-地铁车站及其上盖结构体系的三维有限元模型,利用等效线性化方法考虑土的非线性,以不同类型的单向地震波和双向地震波（含水平向和竖向）作为输入,对土-地铁车站及其上盖结构体系进行了地震反应分析,比较了不同类型地震波作用下地铁车站及其上盖结构体系地震反应的差异,探讨了竖向地震动效应和转换梁刚度的影响．本文的算例结果表明：与普通基岩波和El-centro反演波输入相比较,在长周期基岩地震波作用下地铁车站及其上盖结构体系的内力响应和位移响应均最大．这一地铁车站及其上盖结构体系的薄弱部位位于地铁车站底层第2列、第3列柱的柱端和侧墙与底板连接处．竖向地震动对地铁车站及其上盖结构体系中柱的轴力响应值有较大影响．对于本文的动力计算工况,适当弱化转换梁刚度可降低上盖结构层间位移角的动力响应值．     

隧道下穿地铁拟换乘车站施工监测与安全分析

隧道下穿地铁既有车站为重大风险工程,下穿拟换乘车站时更应进行严格的风险评估与控制,以保证工程施工前后地铁车站的安全运营。本文主要就某新建隧道下穿北京地铁拟换乘车站万寿路站的风险评估和第三方监测进行研究。新建隧道施工可诱发既有车站结构的沉降,造成车站轨道过量变形,进而影响地铁安全运营,本工程采用了结构检测、施工影响模拟预测和第三方监测等工程风险评估和控制手段,结果表明万寿路站受隧道施工影响较小,地铁运营未受影响。     

基于块体单元离散模型的地铁车站爆炸破岩与防护研究

地铁已成为大、中型城市主要交通工具,然而地铁车站一直是恐怖爆炸袭击的重点对象,直接影响地铁运营安全,增强地铁车站结构防护抗爆能力至关重要.本文采用理论分析、数值模拟相结合的研究方法,利用单元内连续、单元间非连续的计算方法,构建块体单元离散弹簧动力学模型,建立地铁车站三维计算模型,模拟地铁车站内部爆炸状况,研究爆炸波空间传播和耗散规律及对构筑物破坏作用;分析低能爆炸作用下车站支柱混凝土、钢管护层混凝土和泡沫钢板夹芯护层混凝土抗爆性能,根据不同防护结构衰减应力波和吸能性能,优化地铁车站构筑物防护结构型式,提高车站抗爆能力,具有重要的实际应用价值.     

Nonnormal Effects in the Taylor–Couette Problem

This work is devoted to the study of transient growth of perturbations in the Taylor–Couette problem due to linear nonnormal mechanisms. The study is carried out for a particular small gap case and is mostly focused on the linearly stable regime of counter-rotation. The exploration covers a wide range of inner and outer angular speeds as well as axial and azimuthal modes. Significant transient growth is found in the regime of stable counter-rotation. The numerical results are in agreement with former analyses based on energy methods and other independent numerical studies. The optimal energy transient growth factor appears to be consistent with experimental observations. This study might shed some light on the subcritical transition to turbulence which is found experimentally in Taylor–Couette flow when the cylinders rotate in opposite directions. Received 13 February 2001 and accepted 29 March 2002 Published online: 2 October 2002 RID="*" ID="*" This work was supported by the UK EPSRC under Grant GR/M30890. The author thanks Nick Trefethen for fruitful discussions. RID="*" ID="*" Present address: Departament de Fisica Aplicada, Univ. Politecnica de Catalunya, 08034 Barcelona, Spain (alvar@fa.upc.es) Communicated by H.J.S. Fernando     

火灾与撞击联合作用下钢管混凝土柱力学性能研究

为研究火灾高温与撞击联合作用下钢管混凝土柱的力学性能,基于ABAQUS建立了高温作用下考虑轴力影响的钢管混凝土柱侧向撞击有限元模型。首先,对高温与撞击联合作用下考虑轴力影响的钢管混凝土柱的破坏模式与受力全过程进行了分析,探讨了高温下钢管混凝土柱的抗撞性能与工作机理;其次,重点研究了受火时间、材料强度、含钢率以及撞击能量对抗撞性能的影响,并给出了相关设计建议。研究结果表明:高温与撞击联合作用下,钢管混凝土柱主要发生受弯破坏;受火15 min后,构件抗撞性能明显降低。轴压力对构件抗撞性能产生不利影响,轴压比从0增加到0.2,受火60 min构件抗撞性能下降了7.8%;混凝土强度对高温下钢管混凝土柱抗撞性能有显著影响,受火90 min后,混凝土强度由30 MPa增加到50 MPa,构件抗撞性能提高约85%;外钢管强度与含钢率对高温下抗撞性能影响不大。     

Theoretical and Numerical Investigation of Flow Transition in Rotating Curved Annular Pipes

Flows in rotating curved annular pipes are investigated by employing a theoretical and numerical method. The numerical results and the perturbation solutions confirm each other. The variations of the flow structure, including the secondary flow and the axial flow, with the force ratio (the ratio of the Coriolis force to the centrifugal force), the curvature and the radius ratio (the ratio of the radius of the inner circle to the radius of the outer circle of the annular pipe) are discussed in detail. The nature of the wall shear stress and the friction factor ratio are also shown. This study is the first to shows the flow transition of the flow in a rotating curved annular pipe and covers large ranges of parameters. Many interesting and previously unreported flow characteristics are obtained. Received 4 February 2002 and accepted 21 May 2002 Published online 30 October 2002 RID="*" ID="*" This research was supported by the Department of Energy under Contact Number W-7405-ENG-36. Communicated by H.J.S. Fernando     

建筑物内火灾烟羽流和顶蓬射流诱发的空气运动盐水模拟实验研究

盐水在清水中的扩散与火灾烟气在空气中的蔓延相似，因而可用盐水的扩散来模拟火灾烟气的蔓延；同样地，由于盐水的扩散而导致的环境清水的运动也可用来模拟烟气蔓延诱发的空气运动。基于这一原理，本文用实验的方法，研究了建筑物内初起火灾产生的烟羽流和顶蓬射流所诱发的空气运动，并对走廊空气层生长规律和运动特性进行了初步的测量和分析。所得结果基本合理，对建筑物通风排烟及疏散通道设计有帮助，从而为建筑火灾环境空气的运动的实验研究开辟了新的思路，也为火灾区域模拟提供了实验依据     

Robust reliable sampled-data control for offshore steel jacket platforms with nonlinear perturbations

In this article, we consider the robust reliable sample-data control problem for an offshore steel jacket platform with input time-varying delay and possible occurrence of actuator faults subject to nonlinear self-exited hydrodynamic forces. The main objective of this work is to design a state feedback reliable sample-data controller such that for all admissible uncertainties as well as actuator failure cases, the resulting closed-loop system is robustly exponentially stable. By constructing an appropriate Lyapunov–Krasovskii functional and using linear matrix inequality (LMI) approach, a new set of sufficient condition is derived in terms of LMIs for the existence of robust reliable sample-data control law. In particular, the uncertainty under consideration in system parameters includes linear fractional norm-bounded uncertainty. Further, Schur complement and Jenson’s integral inequality are used to substantially simplify the derivation in the main results. More precisely, the controller gain matrix for the nonlinear offshore steel jacket platform can be achieved by solving the LMIs, which can be easily facilitated by using some standard numerical packages. Finally, a numerical example with simulation result is provided to illustrate the applicability and effectiveness of the proposed reliable sampled-data control scheme.     

Numerical simulation of the dynamics of free-burning flames,fire whirls,and firestorms.

The paper presents the results of testing a promising package of mathematical models for predicting the dynamics of certain formations in free burning fires, based on a generalized system for time-dependent two-dimensional compressible viscous turbulent gas flows taking combustion into account. The dynamics of flames and fire whirls is investigated using the control volume method. For the first time, firestorms occurring during large fires are numerically simulated; this phenomenon is initiated by the convection of the background vertical component of the atmospheric circulation in the fire influence zone.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 52–61, November–December, 1994.     

Saddle-node bifurcation in the buck converter with constant current load

Occurrence or non-occurrence of saddle-node bifurcation in a buck converter with constant current load under current or voltage mode control is analyzed. The bifurcation critical conditions are derived. The required compensating ramp slope to avoid the bifurcation is also derived. The derived condition is useful to design a stable buck converter as a light emitting diode (LED) driver to avoid the bifurcation. The bifurcation occurs only in some control schemes. When the control scheme makes the converter operate like a current source, the bifurcation occurs. When the control scheme makes the converter operate like a voltage source, the bifurcation does not occur.     

Study on mechanical characteristics and safety evaluation method of steel frame structure after fire

Mechanical characterization of steel frame structure after fire are analyzed based on fire dynamics, heat transfer theory, structural mechanics, and finite element theory. We study the temperature characteristics and mechanical properties of steel frame structure under different fire locations and propose a safety evaluation method. We also analyze damage level of main frame components, maximum temperature of fire, thermal characteristics of frame components, firing duration, etc. to provide useful information for fire resistance design of the steel frame structure and post-disaster safety evaluation.     

崇文门站施工允许地表沉降及三维有限元模拟分析

建设中的北京地铁五号线崇文门站下穿既有地铁一号线区间隧道,为保证既有地下铁道正常运营和地下结构的安全,需严格控制新建车站施工引起的地层位移。结合新建车站暗挖施工及既有线地铁的实际情况,分析和计算穿越既有隧道施工地表允许沉降值。为了控制地表沉降,确保施工安全,拟采用小刚度管棚或大刚度顶管作超前预支护,用3D-S igm a三维有限元软件进行施工效应的计算模拟,掌握大管棚和顶管预支护洞室的力学效应,预测车站施工引起既有隧道的沉降量。最后分析比较两种预支护的支护效果,为选择合理的预支护方案提供参考。     

Three-Dimensionality of Trajectories of Experimental Tracers in a Steady Axisymmetric Swirling Flow: Effect of Density Mismatch

The motion of tracer particles used for visualization in a steady axisymmetric swirling flow in a closed rotating disk cylinder system is studied numerically. It is assumed that there exists a density mismatch between the particles and the fluid. It is shown that such a slight density mismatch leads to a deviation of the particle motion from steady axisymmetric streamlines, which in its turn yields non-axisymmetric patterns of the visualized flow. This gives a possible explanation for an existing disagreement between several experimental and numerical studies. Received 5 November 2001 and accepted 29 March 2002 Published online: 2 October 2002 RID="*" ID="*" This research was supported by the Israel Science Foundation under Grant 240/01, by the Israel Ministry of Immigrant Absorption (to A. Gelfgat), the Israel High Performance Computer Unit, and by the Winograd Chair of Fluid Mechanics and Heat Transfer at Technion. Communicated by H.J.S. Fernando     

Low-complexity robust tracking of high-order nonlinear systems with application to underactuated mechanical dynamics

This paper presents a low-complexity design approach with predefined transient and steady-state tracking performance for global practical tracking of uncertain high-order nonlinear systems. It is assumed that all nonlinearities and their bounding functions are unknown and the reference signal is time varying. A simple output tracking scheme consisting of nonlinearly transformed errors and positive design parameters is presented in the presence of virtual and actual control variables with high powers where the error transformation technique using time-varying performance functions is employed. Contrary to the existing results using known nonlinear bounding functions of model nonlinearities, the proposed tracking scheme can be implemented without using nonlinear bounding functions (i.e., the feedback domination design), any adaptive and function approximation techniques for estimating unknown nonlinearities. It is shown that the tracking performance of the proposed control system is ensured within preassigned bounds, regardless of high-power virtual and actual control variables. The motion tracking problem of an underactuated unstable mechanical system with unknown model parameters and nonlinearities is considered as a practical application, and simulation results are provided to show the effectiveness of the proposed theoretical result.     

Cross-Stream Vorticity Field Induced by Streamwise Vortices in Unbounded and Wall-Bounded Shear Flows

This computational study examines the unsteady cross-stream vorticity structures that form when one or more streamwise vortices are immersed in homogeneous and boundary-layer shear flows. A quasi-two-dimensional limit is considered in which the velocity and vorticity fields, while still possessing three nonzero components, have vanishing gradient in the streamwise direction. This idealization is suitable to applications such as streamwise vortices that occur along a ship hull or airplane fuselage and it can be used as an idealized representation of the quasi-streamwise vortices in the near-wall region of a turbulent boundary layer. In this quasi-two-dimensional idealization, the streamwise velocity has no effect on the cross-stream velocity associated with the vortex. However, the vortex acts to modify the cross-stream vorticity component, resulting in regions of the flow with strong deviations in streamwise velocity. This paper examines the complex structures that form as the cross-stream vorticity field is wrapped up by the vortex and the effect of these structures on the streamwise velocity field, first for vortices immersed in homogeneous shear flow and then for vortices immersed in a boundary layer along a flat wall. Received 2 January 2002 and accepted 13 August 2002 Published online 3 December 2002 RID="*" ID="*" This project was supported by the Office of Naval Research under Grant Number N00014-01-1-0015. Dr. Thomas Swain is the program manager. Communicated by T.B. Gatski