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在标准化结构反应谱时,需要准确地确定地面地震动峰值。而在地震期间,测量地面运动时采集到的地震动加速度时程数据由于种种原因存在基线漂移问题,导致所测数据不能真实反映地面运动．由此难以确定真实地面运动峰值。通过对地震动加速度数据拟合,根据拟合后的数据计算地震速度及位移．并将计算结果分别与利用已有基线修正方法求得的速度及位移进行对比．从而确定最佳拟合次数,消除基线漂移造成影响。研究结果表明,经12次拟合修正地震动加速度求得的地震动位移峰值可用于相对位移反应谱标准化。 相似文献
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在PEER地震动数据库(PGMD)的基础上, 结合近几年国内外特大地震的地面运动记录, 建立了地面运动数据库, 同时根据日本MW9.0特大地震获得的141组记录进行统计回归建立加速度反应谱衰减关系, 并采用条件均值反应谱法, 即设定地震与结构概率需求结合的方法选择地面运动. 选波实例表明, 当设定地震为特大地震时, 基于条件均值反应谱法选取地面运动记录时, 扩展数据库中大震记录并建立符合大震记录加速度反应谱的衰减关系是十分必要与迫切的. 该思路为进一步研究结构动态时程分析中地面运动记录选取问题及所选记录提供了依据. 相似文献
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在PEER地震动数据库(PGMD)的基础上,结合近几年国内外特大地震的地面运动记录,建立了地面运动数据库,同时根据日本Mw 9.0特大地震获得的141组记录进行统计回归建立加速度反应谱衰减关系,并采用条件均值反应谱法,即设定地震与结构概率需求结合的方法选择地面运动.选波实例表明,当设定地震为特大地震时,基于条件均值反应谱法选取地面运动记录时,扩展数据库中大震记录并建立符合大震记录加速度反应谱的衰减关系是十分必要与迫切的.该思路为进一步研究结构动态时程分析中地面运动记录选取问题及所选记录提供了依据. 相似文献
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利用模拟记录和2011年日本东北MW9.0大地震观测记录分析了基于移动窗解卷积法识别场地非线性时变特征的可行性,并与移动窗谱比法的结果进行了对比分析。研究表明:基于移动窗解卷积法可以较好地揭示场地非线性随地震动水平的变化过程,识别非线性发生的阈值、非线性变化程度及强震动后的恢复程度;与移动窗谱比法相比,移动窗解卷积法更容易获得较为稳定的土体非线性时变过程,但对于存在强阻抗比的浅表层土体,移动窗谱比法可以获得更准确的非线性程度。对2011年日本东北MW9.0大地震中8个KiK-net台站进行了非线性时变分析,结果表明;两种方法识别的非线性阈值较接近,约在40—100 cm/s2之间,且与场地vS30没有明显的相关性;在峰值加速度PGA较低的IBRH20台站,非线性引起的波速下降较小（3%）且震后几乎完全恢复;PGA 处于386—822 cm/s2之间的其余7个台站,场地等效剪切波速下降13%—37%,产生了显著的场地非线性,且震后未完全恢复;PGA大于380 cm/s2时,非线性所导致的场地波速下降、恢复与PGA无明显相关性。 相似文献
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《地震工程与工程振动》2017,(6)
基于三维有限元数值模拟对单一浅埋软弱立方体夹杂对地面运动的影响进行研究。通过谱比曲线分析了浅埋软弱夹杂及深宽比对地面运动的放大作用,并分析了夹杂对加速度峰值和反应谱的影响。最后,与二维有限元数值模拟结果进行比较。结果表明:软弱夹杂对R0.85l区域的地面运动放大作用明显,地面运动最大点位于夹杂中心在地表的投影处;当深宽比较小时(N≤1/2),夹杂会对地面运动产生较大的放大作用,当深宽比N≥1时夹杂对地面运动无明显的放大作用,深宽比N=1/16时对地面运动的最大放大倍数是无夹杂自由场的4.2倍;二维模型下夹杂对地面运动放大的频段范围要比三维的宽,放大倍数要比三维的小。 相似文献
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四能窗稳谱技术在岩性密度测井仪中的应用 总被引：1，自引：0，他引：1
在岩性密度测井仪中使用的两能窗稳谱技术存在稳谱耗时长、效果不稳定,特别是在低密度岩层易使高压值跟踪在伪平衡点上等问题。四能窗稳谱处理技术使用线性近似基线谱校正本底或Compton散射伽马等对稳谱窗计数的影响;采用自适应递归数字时间延迟滤波,并根据纵向分辨率和测速的要求,通过测井实践得出了比较合理的稳谱调度周期和帧数;构建了合适的稳谱状态因子与高压调节增量之间的函数关系,克服了两能窗稳谱技术存在的不足。实际应用表明该技术原理正确,实施方法可行、有效。 相似文献
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本文用错格实数傅里叶变换的拟谱法的数值模拟方法分析了地震波在冲积扇、盆地等不均匀地震构造体区域的传播过程和地面运动分布. 结果表明, 地震波由岩石区进入盆地结构后,在盆地内上下多次反射振荡,对地面建筑物可能形成多次连续的振动和破坏,仅有极少量地震波能量返回岩石区域中,这是防灾研究中值得注意的地面运动特征;地震波在盆地边界地质构造条件下,形成的地震波体波与次生面波动的叠加干涉形成了大振幅的地面运动,它可能导致建筑物的极大破坏;破坏峰值的空间位置可能远离岩石和盆地沉积层的边界或者地震断层的位置. 相似文献
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Gtz Schroth Luciana Ferreira Da Silva Marc‐Andree Wolf Wenceslau Geraldes Teixeira Wolfgang Zech 《水文研究》1999,13(10):1423-1436
The partitioning of rain water into throughfall, stemflow and interception loss when passing through plant canopies depends on properties of the respective plant species, such as leaf area and branch angles. In heterogeneous vegetation, such as tropical forest or polycultural systems, the presence of different plant species may consequently result in a mosaic of situations with respect to quantity and quality of water inputs into the soil. As these processes influence not only the water availability for the plants, but also water infiltration and nutrient leaching, the understanding of plant effects on the repartitioning of rain water may help in the optimization of land use systems and management practices. We measured throughfall and stemflow in a perennial polyculture (multi‐strata agroforestry), monocultures of peach palm (Bactris gasipaes) for fruit and for palmito, a monoculture of cupuaçu (Theobroma grandiflorum), spontaneous fallow and primary forest during one year in central Amazonia, Brazil. The effect on rain water partitioning was measured separately for four useful tree species in the polyculture and for two tree species in the primary forest. Throughfall at two stem distances, and stemflow, differed significantly between tree species, resulting in pronounced spatial patterns of water input into the soil in the polyculture system. For two tree species, peach palm for fruit (Bactris gasipaes) and Brazil nut trees (Bertholletia excelsa), the water input into the soil near the stem was significantly higher than the open‐area rainfall. This could lead to increased nutrient leaching when fertilizer is applied close to the stem of these trees. In the primary forest, such spatial patterns could also be detected, with significantly higher water input near a palm (Oenocarpus bacaba) than near a dicotyledonous tree species (Eschweilera sp.). Interception losses were 6·4% in the polyculture, 13·9 and 12·3% in the peach palm monocultures for fruit and for palmito, respectively, 0·5% in the cupuaçu monoculture and 3·1% in the fallow. With more than 20% of the open‐area rainfall, the highest stemflow contributions to the water input into the soil were measured in the palm monocultures and in the fallow. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
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M. N. French R. L. Bras W. F. Krajewski 《Stochastic Environmental Research and Risk Assessment (SERRA)》1992,6(1):27-45
A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities. 相似文献
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M. A. Kahn 《洁净——土壤、空气、水》2000,28(2):95-101
Red tide, a recurrent phenomenon has become conspicuous in several Kashmir lake ecosystems since 1991. The responsible organism (Euglena pedunculata), a rare flagellate rediscovered in the Kashmir Himalaya (Khan 1993) caused first and unprecedented red tide outbreak, constituting a maximum of 96% of resident numerical phytoplankton density in Dal Lake. At present, conflicting hypotheses exist on the generation of causal assemblage(s) imparting redness to waters: Jeeji Bai (1991) linked its origin to acid precipitation – a fallout of burning oil‐fields during the Gulf War – whilst Khan (1993) holds local factor(s) responsible. Field/experimental studies support the latter contention that the influx of untreated sewage, in unison with warm temperatures, high levels of PhAR, iron and interruption to hydrological flow‐pattern together with absence/or reduction in grazing activity created conducive environmental milieu for red tide outbreak. Dal Lake “red tide” drifted the bloom‐inoculum to other waters, including Lake Wular, where additional ecological niches were carved out, threatening the aesthetic value and biological diversity of Kashmir lakes. Ecological monitoring indicates frequent seasonal red tide occurrence in Dal Lake (including summer‐autumn event of 1998) which testifies its unabated eutrophication status. Further studies are needed on ecological adaptability and biogeographic distribution of this rare and unique red tide‐causing flagellate. 相似文献
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