覆水场地地震反应分析

随着各种海洋结构物的兴建,覆水场地的地震反应逐渐成为研究热点。基于任意拉格朗日-欧拉描述,推导时变区域上的流体运动方程,给出流场、结构的接触条件和流场网格运动控制方法。对于平坦覆水场地,水平向地震动作用下,根据Couette流理论证明该类场地流体作用可以忽略;竖向地震动激励下,横向均匀场地可以通过动水压力公式准确考虑流体作用,横向非均匀场地则需要通过流固耦合方法考虑流体作用,以海底隧道为例加以说明。对于起伏场地,天然起伏场地在地震动激励下的动力反应具有明显的流固耦合特征,以三角形起伏场地为算例;结构物的兴建造成的人工起伏场地同样需要考虑流固耦合效应,以某沉管隧道在水平向地震动激励下的动力反应为算例,并根据结果初步提出该类结构物流固耦合分析的简化计算方法。     

盾构隧道的开挖模拟及地震反应数值分析

由于盾构隧道掘进的特殊施工工艺,使开挖模拟的数值计算存在着诸多难以量化的因素。采用应力释放法模拟盾构隧道的开挖,在衬砌和土体之间设置等代层单元模拟盾构施工的影响,求得竣工期的应力场和位移场。在静力计算基础上运用动力有限元时程分析法,采用粘性人工边界条件,分析了隧道衬砌在地震过程中的最大响应。其结果和规律可为一般的盾构隧道地震反应分析提供借鉴。     

考虑荷载修正的衬砌背后空洞对结构安全性影响分析

以云南省某公路隧道为背景,建立考虑空洞影响下的荷载-结构修正计算模型,引入最小安全系数,对衬砌安全性进行评估.计算结果表明:背后存在空洞时,衬砌受力条件恶化,空洞处衬砌内力重分布明显,弯矩分布形态发生改变,导致衬砌安全性显著降低.拱顶或拱腰背后存在空洞时,衬砌最小安全系数均随空洞范围变大而降低.相同空洞范围下,相较于拱...     

Emissions of volatile hydrocarbons from floating roof tanks and their local dispersion: Considerations for normal operation and in case of damage

This work investigates the release and dispersion of volatile organic hydrocarbons, which may escape from external floating roof tanks (EFRT) during normal operation or in case of damage. The dispersion will be described using CFD simulations in close range of the EFRT where hazardous areas are assigned. The aim of this work is to investigate which events can lead to emissions in dangerous quantities and to estimate the corresponding likelihood with regard to explosion protection. An emission in hazardous amount is present if the lower explosion limit has been exceeded and if the extent of this emission is not too low. It is discussed in particular whether the used zoning of potentially explosive areas is conservative or over-conservative.     

盾构铁路隧道坡度对火灾烟气蔓延的影响研究*

为研究坡度隧道内列车阻滞后的火灾烟气蔓延行为，利用火灾动力学模拟软件（FDS）建立盾构铁路隧道火灾模型和CRH6高速列车阻滞模型，隧道坡度分别为0%、1.0%、1.5%、2.0%、2.5%、3.0%、3.5%和4.0%，通过分析隧道内烟气、温度、能见度等特征参数的变化规律，研究坡度隧道内高温烟气的受力情况，探讨坡度变化对火灾烟气蔓延的作用机理。结果表明，坡度隧道内发生火灾，随着烟气的蔓延，隧道内形成沿坡度方向的烟囱效应力，使得烟气在火源两侧呈不对称分布。火源下游区域的高温烟气在火风压和烟囱效应的协同作用下蔓延速度比上游更快，下游烟气层分界中性面与隧道轴线平行，上游烟气层分界中性面呈现水平状态。有坡度的铁路隧道内发生火灾，建议向火源下游方向施加纵向机械通风，人员向火源的上游方向疏散逃生更安全。     

两个相邻高建筑物周围的风环境

描述研究了建筑物周围人行道高度风速分布特征的风洞模拟实验。结果表明：在一个横风向宽度很大的高大建筑物的迎风面拐角附近，风速增大约１倍；而在建筑物的前方有风速的骤变区，这均形成严重的风环境问题。当用一通道将该建筑物分割成两个相邻建筑物时，上述两方面的风环境问题得到了有效的改善，且通道宽度与建筑物顺风向尺度之比的优化数值在１８至２４之间     

低层大气中固体粒子运动及其物理模拟

对于大气边界层中的固体粒子的风致运动－较大粒子的蠕动跃动和较小粒子悬浮－的主要特征作了介绍，着重介绍了在悬浮粒子运动的物理模拟研究方面的一些成果；复杂地形物低层大气湍流会显地提高起尘速率并改变降尘量的分布；有一定我向厚度的风障除了屏蔽效应－－即背风侧平均风速的减小－－外，还滕了终进入空气的灰尘数量的“宏观吸附效应”；总结了模拟悬浮粒子运动的风洞实验所应遵循的相似性准则，并提出了模拟防尘风障的中的     

Estimating fugitive dust emission rates using an environmental boundary layer wind tunnel

Emissions from fugitive dust due to erosion of “natural” wind-blown surfaces are an increasingly important part of PM₁₀ (particulate matter with sizes of 10 μm aerodynamic diameter) emission inventories. These inventories are particularly important to State Implementation Plans (SIP), the plan required for each state to file with the Federal government indicating how they will comply with the Federal Clean Air Act (FCAA). However, techniques for determining the fugitive dust contribution to over all PM₁₀ emissions are still in their developmental stages. In the past, the methods have included field monitoring stations, specialized field studies and field wind-tunnel studies. The measurements made in this paper allow for systematic determination of PM₁₀ emission rates through the use of an environmental boundary layer wind tunnel in the laboratory. Near surface steady-state concentration profiles and velocity profiles are obtained in order to use a control volume approach to estimate emission rates. This methodology is applied to soils retrieved from the nation's single largest PM₁₀ source, Owens (dry) Lake in California, to estimate emission rates during active storm periods. The estimated emission rates are comparable to those obtained from field studies and lend to the validity of this method for determining fugitive dust emission rates.     

Wind Tunnel Experiments and Numerical Simulation of Snow Drifting around an Avalanche Protecting Dam

To learn about wind flow and snow drifting around avalanche dams, experiments were done in the Jules Verne Climatic Wind Tunnel. The paper reports the results from numerical wind flow simulations that were done to support the findings from the wind tunnel. Satisfying the model similitude criteria for the wind tunnel configuration was difficult due to the inevitable small geometric scale of the model, while on the contrary the snow drifting conditions in the facilities were full scale. By comparing numerical wind flow results of full scale and model scale dams with the snow pattern observed in the wind tunnel, it was possible to conclude that albeit poor model similitude, the snowdrifts on the windward side of the wind tunnel model are likely to indicate the full scale natural situation.     

Estimation of the surface stress from the streamwise pressure gradient: The Kármán Integral Momentum Equation revisited

A method is developed to estimate the stress at the surface in a portable wind tunnel for wind erosion studies. The boundary layer height and the pressure gradient are used in a simple expression from the Kármán Integral Momentum Equation. Values of friction velocity u _* are within 10% of experimental values obtained through correlation techniques, including measurements of differential pressures with the Murdoch Turbulence Probe MTP and the X-wire, hot-wire anemometer XWA. Wind velocity and stress profiles reveal logarithmic trends and a constant stress layer near the surface in the DAWA portable wind tunnel. Realignment of the statistics with the mean wind is essential.