建筑工地的雷电防护措施

随着我国经济的快速发展,城市建设规模越来越大,建筑工地雷击事故时有发生,所造成的损失非常巨大,建筑工地防雷显得尤为重要.本文从发生事故主、客观原因人手分析,对如何避免建筑工地发生电击事故进行了几个方面的探讨.     

“6．26”双阳鹿乡镇雷击伤人事故鉴定分析与启示

本文结合事故现场勘查和气象资料分析对2012年6月26日发生在双阳的一起雷击事故分析鉴定过程进行了论述。通过事故原因分析和鉴定结论得到一些启示,并对农村雷电灾害防御提出了建议。     

一起雷击伤亡事故的分析

本文根据雷电灾害现场实地勘查的结果,结合闪电定位资料、天气雷达回波、地理信息资料以及气象资料,综合分析了2010年6月2日发生在湟中县大磨石沟村雷电灾害事故的天气过程以及造成雷灾事故的成因。得出此次雷击事故是雷电流经崖壁泄放入地时,由于旁侧闪络作用,导致人员伤亡。     

一次雷击事故的调查分析与启示

对某公司发生雷击事故进行现场调查和分析,查出雷击事故发生的原因,得到相应的启示和建议。     

黑龙江省雷电灾害调查及案例分析

1引言雷电是一种大自然释放电现象。雷电引起森林火灾,点燃爆炸物,导致输电线路与电力系统故障,扰乱控制系统的电子设备,对人民生产、生活造成很大影响。2雷电灾害调查的意义雷电灾害调查是在雷电事故产生后,对雷电事故发生现场情况、发生地勘察、现场取证、事故鉴定、评估事故损失并整理出事故发生原因。通过雷电灾害调查及鉴定可以预防同类事故发生可能性,从而为气象部门处理同类事故做出理论依据,同时气象部门对雷电灾害防御工作具有管理权,也为政府制定防灾减灾工作方向。     

气象条件对辽宁省高速公路交通安全的影响研究

选取2010—2015年辽宁地区包含事故位置、等级、发生时间、环境条件等信息的高速公路交通事故数据,采用序关系分析法将事故数量和等级量化为高速公路事故指数。匹配事故发生地点临近的气象站点观测数据,分析了高速事故发生时间特征及与气象要素相关性,并利用气象要素通过逐步回归方法对高速事故指数进行模拟。结果表明:辽宁省高速公路事故高发年份气候特征为降水偏多、日照时数偏少。冬季因天气诱发的高速事故数量最多、平均事故指数最大,其中相对湿度、降水量与冬季事故指数关系最为密切。对事故指数进行预测的结果显示:秋季、冬季重特大级别事故的预测准确率较好,准确率分别达到62.5%和51.3%。     

环氧乙烷储运系统环境风险预测与预防措施

以某化工厂环氧乙烷储运系统发生环境风险事故为例,通过风险识别和源项分析,利用有关技术导则中推荐的模式对发生环境风险事故的后果进行预测,得出环氧乙烷储运系统发生泄漏或爆炸时可能造成轻伤、重伤及死亡影响范围的预测结果;同时从风险防范措施和应急预案两方面对环氧乙烷储运系统提出了防范措施,主要包括环氧乙烷的应急处理措施、围堰及事故池的设置、其他风险防范措施要求、运输风险防范措施和环境风险事故应急预案。通过采取以上防范措施,不仅可以最大程度地降低环氧乙烷储运系统环境风险事故发生的概率,而且可以将环境风险事故发生后对环境可能造成的不良影响降至最低。     

县级气象台站雷电防御及雷击事故的应对

随着地面气象观测自动化设备在浙江省投入业务运行以来，本省地面气象观测业务迎来了有史以来最大的技术革命，同时对台站系统及数据安全提出了更高的要求。其中雷击事故对本省自动站及电脑、网络设备威胁最大，每年因雷击造成系统瘫痪影响资料采集和传输的事件屡见不鲜，具有覆盖面广、发生频繁、破坏力强的特点，还具有一定的突发性。本文从本站发生的一次雷击事故入手，就雷电防御及雷击事故应对两个方面分别进行论述。     

广西农村雷灾事故的原因分析及防御措施

从广西2004年农村地区发生的雷灾事故着手,分析广西农村地区雷灾事故发生的原因并归类,针对其特点提出相应的防御措施。     

一次雷击事故的天气形势及成因

利用天气形势图、雷达资料和闪电定位系统资料,对2007年8月13日下午揭阳市一宗雷击事故的天气条件和成因进行分析,结果表明造成本次雷击事故的强对流天气是由于地面低压槽和高空槽的激发而引起的。发生雷击事故时,闪电频数达到26．3次／min,电流幅值均值为21．2kA,由于发生雷击事故的岐山塔处在雷电高发区,地势突出,具备了先导放电的条件,而且该塔没有任何防雷设施,从而导致了雷击事故的发生。     

Summer dryness in a warmer climate: a process study with a regional climate model

Earlier GCM studies have expressed the concern that an enhancement of greenhouse warming might increase the occurrence of summer droughts in mid-latitudes, especially in southern Europe and central North America. This could represent a severe threat for agriculture in the regions concerned, where summer is the main growing season. These predictions must however be considered as uncertain, since most studies featuring enhanced summer dryness in mid-latitudes use very simple representations of the land-surface processes ("bucket" models), despite their key importance for the issue considered. The current study uses a regional climate model including a land-surface scheme of intermediate complexity to investigate the sensitivity of the summer climate to enhanced greenhouse warming over the American Midwest. A surrogate climate change scenario is used for the simulation of a warmer climate. The control runs are driven at the lateral boundaries and the sea surface by reanalysis data and observations, respectively. The warmer climate experiments are forced by a modified set of initial and lateral boundary conditions. The modifications consist of a uniform 3 K temperature increase and an attendant increase of specific humidity (unchanged relative humidity). This strategy maintains a similar dynamical forcing in the warmer climate experiments, thus allowing to investigate thermodynamical impacts of climate change in comparative isolation. The atmospheric CO ₂ concentration of the sensitivity experiments is set to four times its pre-industrial value. The simulations are conducted from March 15 to October 1st, for 4 years corresponding to drought (1988), normal (1986, 1990) and flood (1993) conditions. The numerical experiments do not present any great enhancement of summer drying under warmer climatic conditions. First, the overall changes in the hydrological cycle (especially evapotranspiration) are of small magnitude despite the strong forcing applied. Second, precipitation increases in spring lead to higher soil water recharge during this season, compensating for the enhanced soil moisture depletion occurring later in the year. Additional simulations replacing the plant control on transpiration with a bucket-type formulation presented increased soil drying in 1988, the drought year. This suggests that vegetation control on transpiration might play an important part in counteracting an enhancement of summer drying when soil water gets limited. Though further aspects of this issue would need investigating, our results underline the importance of land-surface processes in climate integrations and suggest that the risk of enhanced summer dryness in the region studied might be less acute than previously assumed, provided the North American general circulation does not change markedly with global warming.     

Continental vegetation as a dynamic component of a global climate model: a preliminary assessment

A simplified vegetation distribution prediction scheme is used in combination with the Biosphere-Atmosphere Transfer Scheme (BATS) and coupled to a version of the NCAR Community Climate Model (CCM1) which includes a mixed-layer ocean. Employed in an off-line mode as a diagnostic tool, the scheme predicts a slightly darker and slightly rougher continental surface than when BATS' prescribed vegetation classes are used. The impact of tropical deforestation on regional climates, and hence on diagnosed vegetation, differs between South America and S.E. Asia. In the Amazon, the climatic effects of removing all the tropical forest are so marked that in only one of the 18 deforested grid elements could the new climate sustain tropical forest vegetation whereas in S.E. Asia in seven of the 9 deforested elements the climate could continue to support tropical forest. Following these off-line tests, the simple vegetation scheme has been coupled to the GCM as an interactive (or two-way) submodel for a test integration lasting 5.6 yr. It is found to be a stable component of the global climate system, producing only ~ 3% (absolute) interannual changes in the predicted percentages of continental vegetation, together with globally-averaged continental temperature increases of up to + 1.5 °C and evaporation increases of 0 to 5 W m^–2 and no discernible trends over the 67 months of integration. On the other hand, this interactive land biosphere causes regional-scale temperature differences of ± 10 °C and commensurate disturbances in other climatic parameters. Tuning, similar to the q-flux schemes used for ocean models, could improve the simulation of the present-day surface climate but, in the longer term, it will be important to focus on predicting the characteristics of the continental surface rather than simple vegetation classes. The coupling scheme will also have to allow for vegetation responses occurring over longer timescales so that the coupled system is buffered from sudden shocks.     

Numerical analysis of a thermotopographically-induced mesoscale circulation in a mountain basin using a non-hydrostatic model

Summary The boundary-layer wind field during weak synoptic conditions is largely controlled by the nature of the landscape. Mesoscale (sub-synoptic) circulations result from horizontal gradients of sensible heat flux due to variation in local topography, variation in surface-cover, and discontinuities such as land-sea contrasts. Such flows are usually referred to as thermally-driven circulations, and are diurnal in nature and often predictable. In this paper we use a state-of-the-art non-hydrostatic computer model to shed light on the physical mechanisms that drive a persistent easterly wind that develops in the afternoon in the Mackenzie Basin, New Zealand. The easterly – Canterbury Plains Breeze (CPB) – is observed early in the afternoon and is often intense, with mean wind speeds reaching up to 12 m s⁻¹. Although computer modelling in mountainous terrain is extremely challenging, the model is able to simulate this circulation satisfactorily. To further investigate the mechanisms that generate the Canterbury Plains Breeze, two additional idealized model experiments are performed. With each experiment, the effects of the synoptic scale wind and the ocean around the South Island, New Zealand were successively removed. The results show that contrary to previous suggestions, the Canterbury Plains Breeze is not an intrusion of the coastal sea breeze or the Canterbury north-easterly, but can be generated by heating of the basin alone. This conclusion highlights the importance of mountain basins and saddles in controlling near-surface wind regimes in complex terrain.     

A cold air lake formation in a basin — a simulation with a mesoscale numerical model

Summary A formation of a cold air lake in a basin is studied with a mesometeorological model.A dynamic Boussinesq hydrostatic mesoscale numerical model is developed in a staggered orthogonal grid with a horizontal resolution of 1 km and with a varying vertical grid. The topography is presented in a block shape so that computation levels are horizontal.The mesometeorological model is tested in three idealized topography cases (a valley, a single mountain, a basin) and test results are discussed.In an alpine basin surrounded by mountains and plateaus the air is supposed to be stagnant at the beginning of the night. Due to differences in radiation cooling an inversion layer is formed in the basin and local wind circulation is studied by model simulations.With 14 Figures     

Effects of a Fence on Pollutant Dispersion in a Boundary Layer Exposed to a Rural-to-Urban Transition

Simultaneous particle-image velocimetry and laser-induced fluorescence combined with large-eddy simulations are used to investigate the flow and pollutant dispersion behaviour in a rural-to-urban roughness transition. The urban roughness is characterized by an array of cubical obstacles in an aligned arrangement. A plane fence is added one obstacle height h upstream of the urban roughness elements, with three different fence heights considered. A smooth-wall turbulent boundary layer with a depth of 10h is used as the approaching flow, and a passive tracer is released from a uniform line source 1h upstream of the fence. A shear layer is formed at the top of the fence, which increases in strength for the higher fence cases, resulting in a deeper internal boundary layer (IBL). It is found that the mean flow for the rural-to-urban transition can be described by means of a mixing-length model provided that the transitional effects are accounted for. The mixing-length formulation for sparse urban canopies, as found in the literature, is extended to take into account the blockage effect in dense canopies. Additionally, the average mean concentration field is found to scale with the IBL depth and the bulk velocity in the IBL.     

Evaporation from a blanket bog in a foggy coastal environment

Frequent fog severely restricts evaporation from blanket bogs in Newfoundland because it more than halves the radiant energy input, and it eliminates the vapor pressure deficit, resulting in evaporation at the equilibrium rate (average = 0.99 during fog). During these periods, there is no surface resistance to evaporation because the bog has been wetted by fog drip, and although the latent heat flux dominates over sensible heat (average = 0.8), both are small. In contrast, the surface dries during clear periods, increasing the surface resistance to evaporation so that sensible heat becomes more important ( = 1.05). When the mosses are dry, evaporation is below the equilibrium rate ( = 0.87), although the higher available energy ensures that actual evaporation is higher. During clear periods, daily evaporation averaged 2.5 mm, compared to 1.1 and 0.7 mm for fog and rain, respectively. The suppressed evaporation at this site is important in maintaining appropriate hydrological conditions for blanket bog development.     

Parameterization of a momentum source in a tropical cumulus ensemble

Summary An eddy effect of tropical deep convection on the large-scale momentum, resp vorticity budget is investigated. The process is specified by a simple parameterization approach which is based on a concept of rotating clouds exerting a momentum on the large-scale flow. The cloud rotation is associated with the thermal properties of a cloud ensemble by the principle of conservation of potential vorticity. A decomposition of cloud classes is applied in consistency with the thermodynamical parameterization scheme of Arakawa and Schubert (1974).The parameterization is tested with observations of GATE74, Phase III. The data are processed on a B/C-scale grid (55km) in a region within 9N and 16N, and between 21W and 27W, and with a vertical resolution of 41 levels. The parameterization results correspond to the observed patterns, especially in situations with strong large-scale wind shear. The findings suggest that certain large-scalle flow regimes provoke convective scale momentum generation rather than redistributing large-scale momentum by convective circulations.With 10 Figures     

Spatial structure of a jet flow at a river mouth

The present work concentrates on the latest data measured in the Jordan river flow in lake Kinneret. Spectral characteristics of fluctuating velocity components have been obtained and processed. The three-dimensional structure of turbulence along the flow has been described. The main features of the jet flow turbulence in the river mouth are: a) The supply of turbulent energy changes due to different mechanisms along the flow. b) The structure of turbulence formed in the river decays rapidly along the flow, and c) In the sand area and beyond it, a significant generation of turbulent energy occurs. Quantitative estimations of the above effects were carried out.     

Atmospheric dispersion of a heavier-than-air gas near a two-dimensional obstacle

Flow over a two-dimensional obstacle and dispersion of a heavier-than-air gas near the obstacle were studied. Two species, one representing air and the other representing the heavier-than-air gas were treated. Equations for mass and momentum were cast in mass-averaged form, with turbulent Reynolds stresses and mass fluxes modeled using eddy-viscosity and diffusivity hypotheses. A two-equation k- turbulence model was used to determine the effective turbulent viscosity. Streamline curvature and buoyancy corrections were added to the basic turbulence formulation. The model equations were solved using finite difference techniques. An alternating-direction-implicit (ADI) technique was used to solve the parabolic transport equations and a direct matrix solver was used to solve the elliptic pressure equation.Mesh sensitivities were investigated to determine the optimum mesh requirements for the final calculations. It was concluded that at least 10 grid spaces were required across the obstacle width and 15 across the obstacle height to obtain valid solutions. A non-uniform mesh was used to concentrate the grid points at the top of the obstacle.Experimental measurements were made with air flow over a 7.6 by 7.6 cm obstacle in a boundary-layer wind tunnel. Smoke visualization revealed a low-frequency oscillation of the bubble downstream of the obstacle. Hot-wire anemometer data are presented for the mean velocity and turbulent kinetic energy at the mid-plane of the obstacle and the mid-plane of the downstream recirculation bubble. A single hot-wire probe was found to be suitable for determining mean streamwise velocities with an accuracy of 11 %. The downstream recirculation bubble was unsteady and had a length range from 3 to 8 obstacle lengths.The experimental results for flow over the obstacle were compared with numerical calculations to validate the numerical solution procedure. A sensitivity study on the effect of curvature correction and variation of turbulence model constants on the numerical solution was conducted. Calculations that included the curvature correction model gave a downstream recirculation bubble length of 5.9 obstacle lengths while excluding the correction reduced this length to 4.4.In the second part of the study, numerical calculations were performed for the dispersion of a heavier-than-air gas in the vicinity of the two-dimensional obstacle. Characteristics of an adiabatic boundary layer were used in these calculations. The densities of the contaminant gases were 0, 25 and 50% greater than the air density. Calculations were performed with the contaminant injection source upstream and downstream of the obstacle.Use of the pressure gradient model reduced the size of the dense gas cloud by as much as 12%. The curvature correction model also affected the cloud expanse by reducing the effective turbulent viscosity in the downstream recirculation bubble. The location of the injection source had the largest impact on the cloud size. The area of the cloud within the 5 % contour was three times larger for downstream injection than for upstream injection.