共查询到19条相似文献，搜索用时 171 毫秒
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本文通过观察同一水位下各种不同的流量及保持流量不变改变淹没深度时的流态、旋涡及吸气状况,研究了泵站进水口的旋涡特性及旋涡发生、发展的影响因素,得出了旋涡类型随淹没深度的变化规律,就后壁距等边界条件对临界淹没深度的影响进行了试验研究,並导出了临界淹没深度的经验公式。 相似文献
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基于GIS栅格数据的青海省羊智沟洪水动态模拟 总被引：2，自引：0，他引：2
采用德国Gemo公司研发的Floodarea水文动力模型,基于气象和灾情资料,模拟强降水导致的山洪情景下逐小时淹没预警点的动态结果,通过淹没深度与累积雨量的拟合,有效的划分了羊智沟山洪灾害不同淹没深度下的临界雨量阈值。结果表明:1)羊智沟流域降水量呈略递减趋势,变化率为-0.02mm/年,年平均气温呈现上升趋势,变化率约为0.032℃/年。2)逐小时淹没深度与6h累积面雨量拟合关系较好,通过0.001的显著性水平检验。3)通过淹没深度和累计雨量的有效拟合,划分了羊智沟洪水临界雨量阈值,为羊智沟洪水灾害预警提供科学依据。 相似文献
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通过调查区域内乡镇及农户各类财产,对洪湖分蓄洪区东隔堤以东区域7~8月份洪水淹没的经济损失进行了估算。利用GIS/MapInfo对空间信息进行存储、统计分析和制图,结果表明,洪湖分蓄洪区在淹没深度等级为0.5 m时,历时3、69、d的经济损失分别为6.5、9.7、13.8亿元;在淹没深度等级为1.0 m时,历时3、6、9 d的经济损失分别为8.7、11.9、15.6亿元;在淹没深度等级为1.5 m时,历时3、6、9 d的经济损失分别为14.8、17.5、20.0亿元,反映出经济损失随着洪水淹没深度及历时的增长而增大的规律,在空间分布特征上表现为一致性。此结果可为分洪决策提供风险和损失评价依据。 相似文献
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针对导管架受撞击后结构轴向临界载荷发生变化的问题,采用线性屈曲分析模块,模拟分析了凹陷位置、凹陷半径及深度对圆柱壳轴向临界载荷的影响,得出了球冠状凹陷对圆柱壳轴向临界载荷的影响规律。结果表明,承受轴向载荷圆柱壳对缺陷的敏感程度与凹陷位置、半径及深度有关;凹陷位置变化使得轴向临界载荷近似呈现正弦规律,凹陷半径增加使得轴向临界载荷减小,且临界载荷变化率逐渐降低;凹陷深度增加使得轴向临界载荷减小,且临界载荷变化率逐渐增加;圆柱壳对凹陷存在2个最敏感区和2个最不敏感区,这些区域不随凹陷位置、凹陷半径及深度的变化而变化;用Fourier级数拟合凹陷圆柱壳轴向临界载荷计算公式,计算值与仿真结果平均绝对误差是1.5%,满足工程分析的需要。 相似文献
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探讨了气象因素、地下水矿化度、土壤质地及结构、农田灌排条件等对地下水临界深度的影响。通过试验数据制定了干旱盐碱区的地下水临界深度标准,并提出了从盐均衡角度来计算农田排水模数。 相似文献
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基于GIS的洪湖分蓄洪区东分块洪水淹没损失的估算及分析 总被引：2，自引：0，他引：2
通过调查区域内乡镇及农户备类财产，对洪湖分蓄洪区东隔堤以东区域7～8月份洪水淹没的经济损失进行了估算。利用GIS／MapInfo对空间信息进行存储、统计分析和制图．结果表明，洪湖分蓄洪区在淹没深度等级为0．5m时．历时3、6、9d的经济损失分别为6．5、9．7、13．8亿元；在淹没深度等级为1．0m时，历时3、6、9d的经济损失分别为8．7、11．9、15．6亿元；在淹没深度等级为1．5m时，历时3、6、9d的经济损失分别为14．8、17．5、20．0亿元，反映出经济损失随着洪水淹没深度及历时的增长而增大的规律．在空间分布特征上表现为一致性。此结果可为分洪决策提供风险和损失评价依据。 相似文献
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基于FloodArea二维水动力模型、数字高程模型和土地利用数据,以重庆市沙坪坝区为研究区域,对其24h历时5a重现期暴雨雨型进行模拟计算,得到面雨量与淹没水深关系,并根据3个淹没等级计算出内涝隐患点的致灾临界雨量;同时对24h历时的10,20,30,50和100a重现期暴雨雨型进行了模拟,并根据风险矩阵法研制了沙坪坝区城市内涝风险区划图.实验结果表明:FloodArea水文模型在城市内涝对于面雨量和地表径流关系上拟合较好,为城市内涝风险区划计算也提供了物理基础. 相似文献
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西北内陆灌区土壤次生盐渍化与地下水动态调控 总被引：7，自引：0，他引：7
土壤次生盐渍化其成因与地下水水位抬升存在密切关系。土壤次生盐渍化防治的根本措施是调控地下水位。本文在分析灌区土壤次生盐渍化发育特点的基础上,指出地下水临界深度不应是一成不变的,应该采用地下水动态临界深度。文中以天山北麓平原灌区为例,根据多年来土壤改良试验成果,确定灌区地下水临界深度为:解冻始2.0—2.5m,春灌始2.5—3.0m,春灌头水末1.2—1.5m,夏灌末2.0—2.5m,冬灌始2.5—3.0m,冬灌末1.3—1.5m。 相似文献
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储训 《扬州大学学报(农业与生命科学版)》1987,(4)
大型轴流泵流道进口旋涡严重影响水泵的运行。本文根据模型试验结果,提出了流道进口水流条件相似的模拟准则。对流道进口发生旋涡的条件和旋涡形成与发展进行了观测研究,并提出对流道进口进行技术改造,以消除旋涡的措施。 相似文献
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《农业科学与技术》2017,(9)
Flooding/submergence of rice fields is a severe problem in South and South-East Asia, affecting more than 20 million hectares of rice every year. Submergence creates hypoxic or anoxic condition causing poor germination, seedling establishment,and enormous yield loss. Standing water in the field from weeks to months also leads to significant yield losses when large part of aerial tissues is under water. For flash flooding, a rice variety FR1A3 with tolerant gene(SUB1A) was identified. SNORKEL1 and SNORKEL2 have been identified for their ability to survive deep-water flooding by rapid elongation. Submergence stress has also been reported to adversely affect cell division and damage cellular and organelle membranes. Research on antioxidative enzymes response and genes that confer tolerance to prolonged flooding is in progress. Here we review the different anoxia responsive genes and the potential involvement of antioxidative enzymes, such as superoxide dismutase, catalase, ascorbate peroxidase and glutathione reductase, which occur in cells of rice plant exposed to submergence stress. 相似文献
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进行了8种坡度下单个三维山体的模型风洞试验，讨论了山体各位置脉动风速谱的变化规律，以及坡度对脉动风速谱的影响.结果表明：背风面山脚0.8 h高度以下位置，脉动风速功率谱与来流风速谱相比，功率谱峰值明显增大，峰值频率向高频移动，单峰特征明显，频带变窄.除此以外的背风面其他位置、迎风面以及山顶位置的脉动风速功率谱与来流风速谱基本一致.提出了山体背风面脉动风速能量由来流湍流能量和山体尾流涡旋能量构成的思想，将来流脉动风速谱与涡旋谱进行分离，并根据试验数据拟合，提出了保守的涡旋谱的计算公式.根据不同坡度山体的试验，得出了0.5为涡旋产生与否的临界坡度. 相似文献
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Keimer B Dogbrevean F Aksay IA Erwin RW Lynn JW Sarikaya M 《Science (New York, N.Y.)》1993,262(5130):83-86
A detailed small-angle neutron scattering study of the vortex lattice in a single crystal of YBa(2)Cu(3)O(7) was made for a field of 0.5 tesla inclined at angles between 0 and 80 degrees to the crystalline c axis. The vortex lattice is triangular for all angles, and for angles less than or equal to 70 degrees its orientation adjusts itself to maximize the pinning energy to densely and highly regularly spaced twin planes. These observations have important implications for the microscopic flux-pinning mechanism, and hence for the critical current achievable in YBa(2)Cu(3)O(7). For large angles (about 80 degrees) the vortex lattice consists of independent chains in the orientation predicted by anisotropic London theory. 相似文献
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Geologic and palynological evidence for rapid sea level change approximately 3400 and approximately 2000 carbon-14 years ago (3600 and 1900 calendar years ago) has been found at sites up to 110 kilometers apart in southwestern British Columbia. Submergence on southern Vancouver Island and slight emergence on the mainland during the older event are consistent with a great (magnitude M >/= 8) earthquake on the Cascadia subduction zone. The younger event is characterized by submergence throughout the region and may also record a plate-boundary earthquake or a very large crustal or intraplate earthquake. Microfossil analysis can detect small amounts of coseismic uplift and subsidence that leave little or no lithostratigraphic signature. 相似文献
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Quantum confinement of itinerant electrons in atomically smooth ultrathin lead films produces strong oscillations in the thickness-dependent film energy. By adding extra electrons via bismuth alloying, we showed that both the structural stability and the superconducting properties of such films can be tuned. The phase boundary (upper critical field) between the superconducting vortex state and the normal state indicates an anomalous suppression of superconducting order just below the critical temperature, Tc. This suppression varies systematically with the film thickness and the bismuth content and can be parametrized in terms of a characteristic temperature, Tc* (less than Tc), that is inversely proportional to the scattering mean free path. The results indicate that the isotropic nature of the superconductive pairing in bulk lead-bismuth alloys is altered in the quantum regime. 相似文献
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Wang Y Ono S Onose Y Gu G Ando Y Tokura Y Uchida S Ong NP 《Science (New York, N.Y.)》2003,299(5603):86-89
We have determined the upper critical field Hc2 as a function of hole concentration in bismuth-based cuprates by measuring the voltage induced by vortex flow in a driving temperature gradient (the Nernst effect), in magnetic fields up to 45 tesla. We found that Hc2 decreased steeply as doping increased, in both single and bilayer cuprates. This relationship implies that the Cooper pairing potential displays a trend opposite to that of the superfluid density versus doping. The coherence length of the pairs xi(0) closely tracks the gap measured by photoemission. We discuss implications for understanding the doping dependence of the critical temperature Tc0. 相似文献