共查询到20条相似文献，搜索用时 125 毫秒
1.
雷击灾害风险评估中等效截收面积计算方法研究 总被引：6，自引：1，他引：5
建筑物等效截收面积的计算直接影响到对该建筑物年预计雷击次数的计算,进而影响到对该建筑物雷击风险评估的准确性。《建筑物防雷设计规范》给出的建筑物等效截收面积的计算方法,适用于高点延伸范围大于低点延伸范围的建筑物等效截收面积的计算,用于计算低点延伸范围大于高点延伸范围的建筑物等效截收面积却不尽合理。鉴于此,提出了优化的计算方法：由建筑物高点和低点计算的等效面积之和,减去滚球法计算出的保护范围面积,得到修正后的等效面积,该方法考虑了中高层建筑的引雷作用,计算结果更接近实际。 相似文献
2.
3.
石湘波王焕邦郑玲沈一平 《内蒙古气象》2016,(3):39-42
文章在雷电灾害风险评估中使用一个恒定的位置因子来计算储罐的截收面积会导致误差的发生,本文根据储罐群以及周边建筑物的分布情况,分析了周边建筑物的高度、相对位置以及其他储罐的环绕程度对储罐截收面积的影响。结果表明:储罐之间距离的远近会使截收面积发生一定的变化,储罐之间间距与截收面积呈正相关;周边建筑物的高度及距离也会造成截收面积计算上的差异;储罐也因环绕程度不同,其截收面积存在不同。 相似文献
4.
从周边建筑物对所考虑建筑物的扩大宽度影响的角度,分析了周边有等高、更低或更高的其他建筑物3种情况下,周边建筑物对所考虑的建筑物截收面积的实际影响.在此基础上提出了周边建筑物的高度、相对位置、环绕程度等均对建筑物截收面积有较大影响,并不能将其乘以一个恒定的位置因子作为考虑了周边建筑物的影响,应根据建筑物所处环境的实际情况的不同做更为精确的计算,以提高风险评估的准确性. 相似文献
5.
6.
分析了规范推荐的架空线路年平均雷击次数计算方法,提出方法中存在截收面积与雷击大地密度对应的雷电流幅值不匹配的问题。为解决该问题,文章以某一具体架空线路为例,介绍了针对全部雷电流幅值,应用积分法计算年平均雷击次数的方法,计算结果与规范推荐方法计算结果的比较说明了积分方法的精密性及结果的合理性。具体的分析、计算方法为：基于电气〖CD*2〗几何模型推导出与雷电流幅值有关的架空线路截收闪电宽度的计算公式,并通过对雷电流幅值频率分布规律的多项式拟合确定任意雷电流幅值的雷击大地密度,任一雷电流幅值对应的截收面积及对应的雷击大地密度的乘积即为该雷电流对应的年平均雷击次数,在该区域雷电流幅值的分布范围内对得到的雷击次数进行积分,即可得到考虑雷电流幅值分布特征的架空线路年平均雷击次数计算结果。 相似文献
7.
8.
9.
10.
1建筑物年预计雷击次数的计算
根据《建筑物防雷设计规范》（下简称规范）第2章的相关条款，规定了建筑物的防雷分类外，同时规定了部分第二、三类防雷建筑物需通过建筑物年预计雷击次数的计算来确定；在工程设计和进行雷击风险评估时，建筑物年预计雷击次数的计算成为必不可少的一个环节。 相似文献
11.
12.
13.
有关大气湍流的几个问题 总被引：3，自引：0，他引：3
浑沌(chaos)概念的提出,有关大气湍流的若干问题有深入讨论的必要。根据我们近几年研究对如下问题提出自己见解,供深入讨论:确定的动力系统可以描述大气湍流,大气湍流可以用有限维动力系统来研究,速度切变?u/?z有两重性,稳定层结下可以出现湍流,Lorenz方程的意义及局限性,湍流发生 相似文献
14.
Carolyn Kousky 《Climatic change》2014,124(1-2):9-20
As sea level rises, coastal communities will face increased risks of flooding, storm surge, and inundation. In some areas, structural protective measures will be built, and for some properties, accommodation to sea level rise may be possible. For other areas, however, some form of retreat will be either preferred on economic or sociopolitical grounds or required given fiscal constraints. This paper considers how society can proactively manage shoreline retreat in those locations where it is deemed the preferable policy. A three-part strategy is proposed: (1) reduce new development in the highest-risk areas; (2) adopt policies that allow for expected and orderly removal or modification of development as inundation occurs; and (3) take advantage of disasters to implement managed retreat approaches. Specific policies are recommended and the challenges of institutional change discussed. 相似文献
15.
利用水平面太阳直接辐射日曝辐量反演大气气溶胶光学厚度的方法研究 总被引：3，自引：1，他引：2
本文发展了一个从宽带水平面太阳直接辐射日曝辐量 (总辐射与散射辐射日曝辐量之差) 反演光谱大气气溶胶光学厚度的方法, 包括建立一个 “等效” 的瞬时太阳天顶角模型, 并提出了一个基于气溶胶标高的云影响甄别方法。对该反演方法的数值模拟和误差分析表明: “等效” 瞬时太阳天顶角模型的不稳定性引起的光学厚度反演误差平均为3.66％; 光学厚度日变化对一段较长时间的平均光学厚度的影响不显著; 订正造成的散射辐射误差≤20％时, 光学厚度平均偏差≤4％。通过与AERONET产品的比对验证表明: 本文发展的光学厚度反演方法和云影响甄别方法都是有效的; 晴空反演的0.75 μm光学厚度与AERONET的相关系数超过0.95, 平均误差约0.02; 云甄别方法计算的季节和年平均光学厚度与AERONET具有较好的一致性。 相似文献
16.
Antti Lauri Joonas Merikanto Evgeni Zapadinsky Hanna Vehkamki 《Atmospheric Research》2006,82(3-4):489
We compare two molecular Monte Carlo simulation methods, the discrete summation method and the growth/decay method, which calculate the vapor-liquid nucleation free energy barrier by simulating isolated clusters of fixed size without the surrounding vapor. The methods are applied to calculations of nucleation barriers of Lennard–Jones argon at 60 K and 80 K. Both of these methods are computationally efficient, as only isolated clusters without the surrounding vapor are simulated, and the methods can be applied with any given cluster definition. They give equivalent results to other methods where the vapor phase is also included. The discrete summation method is based on the calculation of the difference in free energies between two systems containing an n-cluster and an (n − 1)-cluster plus one non-interacting (free) molecule. We show that the configurational space is not equivalent in the two systems. Hence, there has to be an additional term in the free energy calculation that accounts for several kT in magnitude. In contrast to previous studies we also show that it is not correct to prevent the overlap of the non-interacting molecule and another molecule by a zero or an arbitrarily small repulsive potential, but with a small excluded space around the free molecule. 相似文献
17.
Future vegetation changes in thawing subarctic mires and implications for greenhouse gas exchange—a regional assessment 总被引：1，自引：1，他引：0
Julia Bosi? Margareta Johansson Terry V. Callaghan Bernt Johansen Torben R. Christensen 《Climatic change》2012,115(2):379-398
One of the major concerns regarding climate change in high latitudes is the potential feedback from greenhouse gases (GHG) being released from thawing peat soils. In this paper we show how vegetational patterns and associated GHG fluxes in subarctic palsa (peat mounds with a permanently frozen core) mires can be linked to climate, based on field observations from fifteen palsa sites distributed in northern Fennoscandia. Fine resolution (100?m) land cover data are combined with projections of future climate for the 21st century in order to model the potential future distribution of palsa vegetation in northern Fennoscandia. Site scale climate-vegetational relationships for two vegetation types are described by a climate suitability index computed from the field observations. Our results indicate drastic changes in the palsa vegetational patterns over the coming decades with a 97?% reduction in dry hummock areas by 2041?C2060 compared to the 1961?C1990 areal coverage. The impact of these changes on the carbon balance is a decrease in the efflux of CO2 from 130 kilotonnes C y?1 to a net uptake of 11 kilotonnes C y?1 and a threefold increase in the efflux of CH4 from 6 to 18 kilotonnes C y?1 over the same period and over the 5,520?km2 area of palsa mires. The combined effect is equivalent to a slight decrease in CO2-C emissions, from 182 to 152 kilotonnes C y?1. Main uncertainties involve the ability of the vegetation community to adapt to new conditions, and long-term changes in hydrology due to absence of ice and frost heaving. 相似文献
18.
《Atmospheric Research》2007,83(3-4):489-502
We compare two molecular Monte Carlo simulation methods, the discrete summation method and the growth/decay method, which calculate the vapor-liquid nucleation free energy barrier by simulating isolated clusters of fixed size without the surrounding vapor. The methods are applied to calculations of nucleation barriers of Lennard–Jones argon at 60 K and 80 K. Both of these methods are computationally efficient, as only isolated clusters without the surrounding vapor are simulated, and the methods can be applied with any given cluster definition. They give equivalent results to other methods where the vapor phase is also included. The discrete summation method is based on the calculation of the difference in free energies between two systems containing an n-cluster and an (n − 1)-cluster plus one non-interacting (free) molecule. We show that the configurational space is not equivalent in the two systems. Hence, there has to be an additional term in the free energy calculation that accounts for several kT in magnitude. In contrast to previous studies we also show that it is not correct to prevent the overlap of the non-interacting molecule and another molecule by a zero or an arbitrarily small repulsive potential, but with a small excluded space around the free molecule. 相似文献
19.
Julian Ramirez-Villegas Mike Salazar Andy Jarvis Carlos E. Navarro-Racines 《Climatic change》2012,115(3-4):611-628
Policy measures regarding adaptation to climate change include efforts to adjust socio-economic and ecologic systems. Colombia has undertaken various measures in terms of climate change mitigation and adaptation since becoming a party of the Kyoto protocol in 2001 and a party of the United Nations Framework Convention on Climate Change (UNFCCC) in 1995. The first national communication to the UNFCCC stated how Colombian agriculture will be severely impacted under different emission scenarios and time frames. The analyses in this document further support that climate change will severely threaten the socioeconomics of Colombian agriculture. We first query national data sources to characterize the agricultural sector. We then use 17 Global Circulation Model (GCM) outputs to quantify how Colombian agricultural production may be affected by climate change, and show the expected changes to years 2040–2069 (“2050”) under the A2 scenario of the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (SRES-A2) and the overall trends in both precipitation and temperature to 2100. We then evaluate expected changes within different regions and measure the proportion of area affected within each crop’s distributional range. By 2050, climatic change in Colombia will likely impact 3.5 million people, 14?% of national GDP corresponding to agriculture, employment of 21?% of the population, agro-industries, supply chains, and food and nutritional security. If no adaptation measures are taken, 80?% of crops would be impacted in more than 60?% of their current areas of cultivation, with particularly severe impacts in high value perennial and exportable crops. Impacts also include soil degradation and organic matter losses in the Andes hillsides; likely flooding in the Caribbean and Pacific coasts; niche losses for coffee, fruit, cocoa, and bananas; changes in prevalence of pests and diseases; and increases in the vulnerabilities of non-technically developed smallholders. There is, however, still time to change the current levels of vulnerability if a multidisciplinary focus (i.e., agronomic, economic, and social) in vulnerable sectors is undertaken. Each sub-sector and the Government need to invest in: (1) data collection, (2) detailed, regionally-based impact assessments, (3) research and development, and (4) extension and technology transfer. Support to vulnerable smallholders should be given by the state in the form of agricultural insurance systems contextualized under the phenomenon of climate change. A national coordination scheme led by (but not restricted to) the Ministry of Agriculture and Rural Development (MADR) with the contributions of national and international institutions is needed to address agricultural adaptation. 相似文献
20.
The tropical Pacific has begun to experience a new type of El Nio, which has occurred particularly frequently during the last decade, referred to as the central Pacific(CP) El Nio. Various coupled models with different degrees of complexity have been used to make real-time El Nio predictions, but high uncertainty still exists in their forecasts. It remains unknown as to how much of this uncertainty is specifically related to the new CP-type El Nio and how much is common to both this type and the conventional Eastern Pacific(EP)-type El Nio. In this study, the deterministic performance of an El Nio–Southern Oscillation(ENSO) ensemble prediction system is examined for the two types of El Nio. Ensemble hindcasts are run for the nine EP El Nio events and twelve CP El Nio events that have occurred since 1950. The results show that(1) the skill scores for the EP events are significantly better than those for the CP events, at all lead times;(2) the systematic forecast biases come mostly from the prediction of the CP events; and(3) the systematic error is characterized by an overly warm eastern Pacific during the spring season, indicating a stronger spring prediction barrier for the CP El Nio. Further improvements to coupled atmosphere–ocean models in terms of CP El Nio prediction should be recognized as a key and high-priority task for the climate prediction community. 相似文献