基于复杂网络的岩土颗粒材料分散性失稳先兆研究     

杨晓娟  马刚  周恒  陆希  李易奥  周伟 《岩土力学》2022,43(7):1978-1988

岩土颗粒材料在达到Mohr-Coulomb塑性极限之前可能已经发生了没有明显局部损伤的全域准均匀破坏,即分散性失稳。近年来,网络科学工具在颗粒材料环境中的应用为研究其失稳破坏现象提供了有趣新颖的洞见。采用离散单元法对不同初始密实度的颗粒体系进行等体积应变加载路径的数值试验,发现初始状态越松散的颗粒体系越有可能发生分散性失稳;采用网络科学的理论和方法分析颗粒接触网络的拓扑结构特性和演化规律,发现颗粒材料分散性失稳的结构根源是颗粒接触网络完全崩塌。将颗粒体系划分为强、弱接触系统以构建强接触子网络、弱接触子网络和强−弱接触子网络,研究颗粒接触网络及其3个子网络的特征量演化,结果表明：当颗粒材料开始处于不稳定状态时,易受扰动的弱接触系统的部分接触先失效,导致强接触系统失去其稳定支撑作用而降低承载能力。随着加载的继续,系统通过非局部的自组织过程导致接触结构的全面崩塌,最终触发整体分散性失稳。因此,先于整体失稳的部分弱接触的失效,可视为颗粒材料分散性失稳的关键性临界征兆。  相似文献   

裂隙黄土边坡三维稳定性极限分析     

朱学亮  邵生俊  沈晓钧  邵帅  刘小康 《岩土力学》2022,43(10):2735-2743

黄土边坡中竖直裂隙的发育往往会对边坡稳定产生影响。相对于平面应变机制,建立三维破坏机制下边坡稳定性分析方法更能接近实际边坡失稳情况。基于塑性极限分析上限法,考虑预先存在竖直裂隙的三维黄土边坡不同破坏机制（坡面破坏、坡脚破坏和坡底破坏）,建立能量平衡方程及其无量纲临界高度值γH/c表达式,采用随机搜索法得到了临界高度的上限解。分析了约束宽度、边坡坡度、内摩擦角以及裂隙深度对三维竖直裂隙黄土边坡临界高度值的影响。结果表明：对于坡脚破坏机制,临界高度值随着裂隙深度的增加而减小,减小至临界裂隙深度 (δ /H)_min后,裂隙深度的增加不再影响临界高度值;临界裂隙深度随着坡度β 的增大而增大,随着内摩擦角φ 的增大而减小。当约束宽度B/H<0.8时,大多数破坏机制为坡面破坏。当约束宽度B/H=0.8、内摩擦角φ =10° 及约束宽度B/H=0.6、内摩擦角φ =15° 时,边坡的破坏从坡面破坏机制逐渐过渡到坡脚破坏机制。存在竖直裂隙的黄土边坡比完整边坡具有更小的临界高度,约束宽度及内摩擦角会对三维黄土边坡破坏机制产生影响。  相似文献   

俯冲带地震诱发机制:研究进展综述   总被引：4，自引：0，他引：4  

邵同宾  嵇少丞 《地质论评》2015,61(2):245-268

俯冲带作为地球循环体系的关键部位,具有构造活跃、地震多发以及地质条件复杂等特征。基于震源位置,俯冲带地震既可划分为板间和板内地震,也可分为浅源、中源和深源地震。俯冲带内的浅源地震包括板间地震和浅源板内地震,而中源和深源地震皆属于板内地震。在地球浅部,温度与压力低,浅源地震是由岩石发生脆性破裂或沿着先存断层发生不稳定摩擦滑移造成的。随着深度增加,温度和压力的增加使得流行于浅部的脆性和摩擦行为在无水条件下被强烈抑制,岩石从而表现为可抑制地震的韧性行为,使得中-深源地震的诱发机制有别于常规的脆性行为。随着研究的逐渐深入,人们了解到中源地震的诱发机制主要是脱水或与流体相关的致脆以及塑性剪切失稳,而深源地震的成因主要是相变致裂。然而,中-深源地震很可能是两种或两种以上机制共同作用的结果。例如,在中源深度既可能是流体相关的致脆导致脱水源区的脆性围岩产生地震,亦可能是脱水的蛇纹岩本身可能在流体孔隙压的作用下作粘滑滑移,而前者比后者更为重要。孕震带宽度大于"反裂隙模型"预测的亚稳态橄榄石冷核宽度的深源地震可能是由第一阶段的相变致裂和第二阶段的塑性剪切失稳诱发,而孕震带的实际宽度与预测宽度相当的深源地震则可能仅由相变致裂引起。只要过渡带内名义无水矿物中的结构水能释放出来,脱水致脆同样可能触发一些深源地震;而塑性剪切失稳不仅能在中-深源地震触发后的扩展阶段起着主导作用,而且还能单独触发一些中-深源地震,因此能够解释大多数反复发生的中-深源地震活动。  相似文献   

2011年长江中下游旱涝急转及汛期暴雨的对流条件研究     

黄明策  沈新勇  刘会鹏  李小凡 《热带气象学报》2020,36(5):590-602

利用ERA-Interim及雨量和土壤水分观测资料,对比诊断了2011年5—6月长江中下游梅汛前极旱期急转为梅汛期洪涝的极端天气事件的对流条件（水汽、不稳定、抬升作用）差异及特征,并研究条件性湿位涡垂直通量（CMF）指数与暴雨之间的定量关系。结果表明:在极旱期,干冷的东北气流控制,西太平洋副热带高压偏东,低层水汽通量弱且以偏北风输送为主,中低层为下沉气流,无低空急流,等θ_se线稀疏,边界层抬升机制缺乏,是干旱加剧的主要因子;在梅汛期,西南气流增强,西太平洋副热带高压西伸,低层气流在长江地区辐合,低层水汽通量增加且转为西南和东南风输送为主,伴随高低空急流耦合和深厚的上升运动,等θ_se线密集形成梅雨锋,增强不稳定暖湿空气强迫抬升和垂直输送,造成暴雨频发,引起区域性洪涝。暴雨中心600 hPa以下为负湿位涡的不稳定层,对流不稳定与条件性对称不稳定共同作用是强降水发生的不稳定机制。CMF指数与旱涝变化、暴雨过程演变非常一致,在极旱（梅汛）期,CMF指数低（高）,变化平缓（剧烈）,CMF指数在暴雨开始时逐步剧增,结束时迅速减小。   相似文献   

An Empirical Tropical Instability Wave-induced Wind Stress Model in the Equatorial Pacific and its Incorporation into the Ocean Model     

Yanzhou Wei  Xianbiao Kang  Yuhua Pei 《大气与海洋》2013,51(5):350-361

Abstract

Satellite observations revealed that there is a close relationship between perturbations of sea surface temperature (SST) and wind stress (τ) induced by tropical instability waves (TIWs; SST_TIW and τ _TIW). Using the empirical relationship observed between TIW-induced wind stress divergence (curl) and downwind (crosswind) SST gradients, this study establishes a TIW-induced wind stress field perturbation model τ _TIW?=?F(SST). This empirical model solves τ _TIW from the TIW-induced wind stress divergence and curl, which are estimated from the downwind and crosswind SST gradients. This empirical τ _TIW?=?F(SST) model can be incorporated into the ocean model to take into account the effect of τ _TIW. By comparing two experiments with and without the τ _TIW effect, this study demonstrates that τ _TIW has a substantial effect on the equatorial Pacific heat budget and induces the long-term mean SST to exhibit a 0.2°C difference, which is consistent with previous studies.  相似文献   

Axially Symmetric Cosmic Strings in a Scalar-Tensor Theory     

D. R. K. Reddy  R. L. Naidu  V. U. M. Rao 《Astrophysics and Space Science》2006,306(4):185-188

Axially symmetric cosmological models with cosmic string source are obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A113, 467, 1985). The models obtained give us axially symmetric geometric (Nambu) string, p-string and Reddy string (Astrophys. Space Sci. 286, 2003b) in Saez-Ballester theory. Some physical properties of the models are also discussed.  相似文献   

A Two—Temperature Supernova Fallback Disk Model for Anomalous X—ray Pulsars     

Ye Lu  K. S. Cheng National Astronomical Observatories  Chinese Academy of Sciences  Beijing Department of Physics  University of Hong Kong  Hong Kong  China 《中国天文和天体物理学报》2002,2(2):161-168

We present a case study of the relevance of the radially pulsational instability of a two-temperature accretion disk around a neutron star to anomalous X-ray pulsars (AXPs). Our estimates are based on the approximation that such a neutron star disk with mass in the range of 10^-6-10^-5M⊙ is formed by supernova fallback. We derive several peculiar properties of the accretion disk instability: a narrow interval of X-ray pulse periods; lower X-ray luminosities; a period derivative and an evolution time scale. All these results are in good agreement with the observations of the AXPs.  相似文献   

On Motions Near the Lagrange Equilibrium Point L 4 in the Case of Routh's Critical Mass Ratio     

Boris Bardin 《Celestial Mechanics and Dynamical Astronomy》2002,82(2):163-177

We deal with the planar restricted circular problem of three bodies. We study trajectories in a small neighborhood of the Lagrange equilibrium point L ₄ when mass ratio is close to Routh's value. In particular, we show that the case of proper degeneracy takes place and for most initial conditions trajectories are conditionally-periodic. We obtain an approximate representation of families of periodic solution emanating from the equilibrium point L ₄. We also show that in the case of instability of L ₄ the trajectories starting in a vicinity of L ₄ remain in a finite domain forever. We give an upper bound of this domain. To carry out our investigation, we analyze the dynamics of a general Hamiltonian system with two degrees of freedom in the case of 1 : 1 resonance in detail.This revised version was published online in October 2005 with corrections to the Cover Date.  相似文献   

A bivariate gamma distribution for use in multivariate flood frequency analysis     

Sheng Yue 《水文研究》2001,15(6):1033-1045

A gamma distribution is one of the most frequently selected distribution types for hydrological frequency analysis. The bivariate gamma distribution with gamma marginals may be useful for analysing multivariate hydrological events. This study investigates the applicability of a bivariate gamma model with five parameters for describing the joint probability behavior of multivariate flood events. The parameters are proposed to be estimated from the marginal distributions by the method of moments. The joint distribution, the conditional distribution, and the associated return periods are derived from marginals. The usefulness of the model is demonstrated by representing the joint probabilistic behaviour between correlated flood peak and flood volume and between correlated flood volume and flood duration in the Madawask River basin in the province of Quebec, Canada. Copyright © 2001 John Wiley & Sons, Ltd.  相似文献   

Validating the Flash Code: Vortex-Dominated Flows     

Greg Weirs  Vikram Dwarkadas  Tomek Plewa  Chris Tomkins  Mark Marr-Lyon 《Astrophysics and Space Science》2005,298(1-2):341-346

As a component of the Flash Center’s validation program, we compare FLASH simulation results with experimental results from Los Alamos National Laboratory. The flow of interest involves the lateral interaction between a planar M _a = 1.2 shock wave with a cylinder of gaseous sulfur hexafluoride (SF₆) in air, and in particular the development of primary and secondary instabilities after the passage of the shock. While the overall evolution of the flow is comparable in the simulations and experiments, small-scale features are difficult to match. We focus on the sensitivity of numerical results to simulation parameters.  相似文献