共查询到20条相似文献，搜索用时 93 毫秒
1.
四种计算地震反应数值方法的比较研究 总被引：27，自引：9，他引：18
本文在简要总结了计算单自由度系统地震反应频域方法和时域方法的特点之后,按照统一的递归公式,系统地对计算单自由度体系的四种时域方法即中心差分方法、Newmark方法、Z变换方法、Duhamel逐步积分法进行了对比研究。通过递归系数b1和b2的不变性、传递函数的低频约束条件和相位特性以及数值分析等几个方面说明了上述方法各自的优缺点、相对精度和适用的范围。根据动力平衡方程的算子不变性,研究了上述方法的共性特征,揭示了相对位移、相对速度、相对加速度递归公式的内在联系,这表明只要知道相对位移的递归公式,相对速度、相对加速度的递归公式也就随之确定,在此基础上推荐了一套计算单自由度系统相对位移、相对速度、相对加速度地震反应的递归公式。 相似文献
2.
《地震工程与工程振动》2017,(3)
本文简要综述了时域连续Galerkin(TCG),改进TCG,以及时域间断Galerkin(TDG)以及高阶单步法等几种典型的高阶时域积分算法。若采用p阶多项式对基本未知量进行插值近似,采用单场格式的常规TCG算法、改进TCG算法、两场格式的TDG算法求得的位移和速度分别具有p、2p、2p+1阶收敛精度,在计算成本相当的情况下,改进TCG算法具有最高收敛精度。高阶单步法多为后处理的算法,大多具有4阶精度。相比最常用的二阶算法,高阶单步法操作简单,易于实施,保留二阶算法无条件稳定、计算效率高等优点,可对二阶算法进行误差估计,并可根据精度需求,指导时间步长自适应调整。 相似文献
3.
线性系统在非平稳随机激励下的响应 总被引：1，自引：0，他引：1
本文通过广义复模态理论把动力学方程降阶,使系统的脉冲响应函数和传递函数具有简单的形式,在此基础上讨论了一般线性系统在演变非平稳随机激励下响应计算的频域法和时域法。通过算例对频域法和时域法进行了比较,并对单自由度体系演变非平稳响应的谱矩进行了研究。 相似文献
4.
5.
本文提出了一种全新的基于等效Q值的时域反Q滤波算法,其允许等效Q值在垂向上随时间连续变化,在空间上存在弱变化;将加权最小平方方法优化设计思想引入到时域反Q补偿短算子设计当中,给出最优时域短算子设计,将大量的频率域乘法工作转化为少量的时域褶积运算;采取表驱动方案,将短算子的构建与反Q补偿运算相剥离,极大地提升了计算效率;提出了一种新的稳定性控制方法,其既保证算法具有良好的稳定性,又满足短算子设计精度的要求.数值计算表明：时域反Q滤波算法可以取得与频域算法相同的补偿效果,并保证算法具备良好的稳定性和较高的计算效率. 相似文献
6.
7.
有阻尼体系动力问题的一种显式差分解法 总被引：15，自引：7，他引：15
本文以中心差分方法为基础,结合Newmark常平均加速度法的基本假定,推导出了一种求解有限自由度有阻尼体系动力方程的自起步显式差分格式。此格式的稳定性条件与一般中心差分格式的相当,其计算精度不低于二阶精度。 相似文献
8.
复阻尼模型的时域运动方程通解中包含有发散项,导致传统的逐步积分法计算结果不能稳定收敛。为克服该缺点,引入地震加速度在时间步长内是线性变化的假定,利用复化对偶原则,提出了复阻尼模型的时域数值计算方法,可在时间步长内剔除发散项,保证了时域计算结果的稳定收敛。在此基础上,结合模态叠加法,进一步提出了多自由度体系的时域数值方法。算例分析表明:复阻尼模型的时域数值计算结果与谐波作用下时域解析算法、地震动作用下频域法的计算结果近似相等,证明了方法的正确性;对于钢筋混凝土框架结构,复阻尼模型的时域计算结果与黏性阻尼模型近似相等。 相似文献
9.
非平稳随机振动响应的离散分析方法 总被引：1，自引：0，他引：1
本文提出了一种工程结构离散随机振动分析的新方法。应用这个方法可以方便地求解体系在任意激发下的随机响应。文中给出了两种基本差分格式,研究了它们的稳定性和精确性,并把它们结合起来,构造了一个高精度算法。应用该算法对单自由度体系进行实际计算所得的结果表明:它是令人满意的。 相似文献
10.
对阶跃响应波形的时域测定与频域测定两种方法进行对比计算,结果表明,频域测定法的计算精度提高约1个数量级。研究地震计周期与阻尼参数的影响因素,应优先选用频域测定法。 相似文献
11.
12.
13.
14.
15.
16.
17.
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
18.
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
19.
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