Criteria for assessing dynamic collapse of elastoplastic structural systems     

Y. Araki  K. D. Hjelmstad 《地震工程与结构动力学》2000,29(8):1177-1198

Criteria are presented for assessing the propensity for dynamic collapse of elastoplastic structural systems. To detect the onset of dynamic collapse, three key concepts are introduced. First, the equations of motion are linearized and time shifted relative to a reference time in a dynamic process. Second, we study the free vibration of the system after the reference time. Third, we use a modal decomposition of the response. We suggest that dynamic collapse is likely if (1) there exist negative eigenvalues of the Hessian of the total potential energy and (2) the direction of motion is consistent with the loading direction of the elastoplastic material. The direction of motion is determined by using the gradient of total potential energy and the eigenmodes corresponding to the negative eigenvalues. The fidelity of the present criteria is demonstrated through numerical examples for which the non‐linear equations of motion can be integrated exactly. With the present approach, it becomes apparent that p‐delta effects, the tangent stiffness, the internal resistance, and the direction of unloading all play key roles in the dynamic collapse of structures. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

近60年淮河流域夏季降水的变化特征   总被引：2，自引：0，他引：2  

冯志刚  梁树献  徐胜  徐时进  李文杰 《水文》2019,39(6):85-89

利用淮河流域1961～2017年夏季降水量资料,运用线性回归、滑动平均、Morlet小波、滑动T检验和Lepage检验方法分析了流域夏季降水的周期性特征和年代际变化特征。结果表明:流域夏季降水在大部分时段都具有明显的年际振荡特征,从20世纪90年代开始年代际振荡特征非常突出;流域夏季降水具有2～3a的年际变化周期和18～24a的年代际变化周期,1961～1967年、1997～2006年期间2～3a的短周期振荡非常显著,1990年以后18～24a的周期变得非常明显;在2000年前后,流域33～35°N纬向带状区域发生了显著的年代际突变现象,突变后与之前相比夏季降水增多了40%～60%;在2009年,流域沿淮河一线以北至35°N范围内再次发生显著的年代际突变现象,突变后降水减少了20%以上,此次年代际突变范围更广也更加显著,其物理成因值得进一步研究。  相似文献   

青藏高原东缘非刚性书斜式断层模型的物理模拟实验研究     

刘军  贾东  尹宏伟  沈礼  范小根  杨双 《地质学报》2020,94(6):1780-1792

印度板块和欧亚板块碰撞导致青藏高原垂向上整体快速隆升的同时,也导致东缘被断裂分割的块体沿着大规模走滑断裂的横向滑移,这也是青藏高原演化变形的两种端元模型:大陆逃逸模式和地壳增厚模式。本文设计了三种非刚性书斜式断层模型,运用粒子速度场成像技术(PIV, Particle Image Velocimetry)监测模型表面变形。实验结果表明,非刚性块体边界受力前后,位移场、速度、剪应变和面应变会有明显的不同。根据实验结果主要得出两点结论:①青藏高原东缘的变形是连续的,块体内部发育了冲断带、裂谷系统和右行走滑断裂系统;②自中新世以来,青藏高原东缘主要经历了两阶段的演化,早中新世-晚中新世(22～8Ma),既有左行走滑活动,也有块体的顺时针旋转,形成了近东西向的祁连山-南山冲断带、积石山冲断带、祁漫塔格冲断带、渭河地堑以及近南北向的右行走滑断裂;晚中新世(8Ma)以来,块体旋转量极少,主要以左行走滑断裂为主,发育了近南北向的冲断带和裂谷系统。  相似文献   

不同振动特性参数对振动沉管/压实的影响          下载免费PDF全文

何胜煜  胡远彪  卜长根 《探矿工程》2020,47(11):83-87

振动钻探或沉管/压实机械在工程中有着广泛的应用,但缺乏频率比、阻尼比对振动沉管机械功率影响的系统研究,施工中有时会出现功率异常增大,其驱动功率如何计算仍然困扰着工程设计人员。本文通过阻尼耗散功率法,来分析计算惯性和非惯性激励振动机械的平均功率、瞬时功率问题。结果显示,大阻尼（0.5＜ ζ ＜1）全频率范围的一般情况,惯性激励系统耗散功率近似与激振力角频率平方成正比,仅在小阻尼（阻尼比 ζ ＜0.5）共振区,功率与激振力幅值的平方成正比,与阻尼成反比,正是小阻尼易引起功率异常增大;非惯性激励机械在有阻尼共振区附近工作才能吸收足够的功率。振动沉管机械设计时不仅要满足系统的平均功率的需求,还要校验最大瞬时功率需求。  相似文献   

香港CORS站坐标时间序列分析研究          下载免费PDF全文

陈晨  魏冠军  高志钰  寇瑞雄 《全球定位系统》2019,44(2):89-97

针对不同地区连续运行参考站(CORS)坐标时间序列周期特性与噪声特性存在的差异性问题,本文采用功率谱分析法和极大似然法分析香港卫星参考站网(SatRef)的坐标时间序列.研究结果表明,参考站点的三个坐标分量上都存在明显的年周期项与半年周期项.各参考站坐标分量上的噪声特性存在多样化的特征,白噪声(WN)加闪烁噪声(FN)是主要噪声模型,仅考虑WN而忽视有色噪声(CN)的做法会大大低估参数估计的不确定度.根据最优噪声模型估值得出的SatRef站速度场在水平方向上有整体向东南方向运动的趋势,与华南块体的运动结果基本一致.  相似文献   

Research of photolithography technology based on surface plasmon     

李海华  陈健  王庆康 《海洋学报(英文版)》2010,29(11)

This paper demonstrates a new process of the photolithography technology, used to fabricate simply fine patterns, by employing surface plasmon character. The sub-wavelength periodic silica structures with uniform silver film are used as the exposure mask. According to the traditional semiconductor process, the grating structures are fabricated at exposing wavelength of 436 nm. At the same time, it provides additional and quantitative support of this technique based on the finite-difference time-domain method. The results of the research show that surface plasmon characteristics of metals can be used to increase the optical field energy distribution differences through the silica structures with silver film, which directly impact on the exposure of following photosensitive layer in different regions.  相似文献   

Effects of Planting Field on Groundwater and Surface Water Pollution in China     

Yaa Opoku‐Kwanowaa  Rachel Kasoro Furaha  Li Yan  Daming Wei 《洁净——土壤、空气、水》2020,48(5-6)

Water forms an essential resource for life on earth because all living things on earth depend on water for life activities. However, with the increase in the human population, which is coupled with intense urbanization and agricultural activities, global water pollution has increased over the past decades. In China, agricultural activities that occure mainly in the planting fields have been listed as the main source of surface water and groundwater pollution. This review focuses on the major factors that influence pollution from planting fields in China mainly as a result of farming activities such as flood irrigation, excessive application of fertilizers and pesticides, and poor management practices. At present, good results are achieved by adopting soil fertilization test formula, biodegradable pesticides, proper irrigation, and agroforestry interventions. In the future, pollution from planting fields as a non‐point source of water pollution can be improved and resolved by perfect nutrient management, best management practices, organic amendments, restoring water environment, and intelligent assessment management.  相似文献   

In Situ Bioremediation of Toluene‐Polluted Vadose Zone: Integrated Column and Wetland Study     

Shreejita Basu  Brijesh Kumar Yadav  Shashi Mathur  Pankaj Kumar Gupta 《洁净——土壤、空气、水》2020,48(5-6)

A vertical soil column setup integrated with wetlands is developed to study the biodegradation and transport of toluene, a light non‐aqueous phase liquid (LNAPL), in the subsurface environment. LNAPL‐contaminated water is applied to infiltrate from the top of the soil column. The observed and simulated breakthrough curves show high equilibrium concentration at top ports rather than at lower ports, indicating effective toluene biodegradation with soil depth. The observed equilibrium concentration of toluene is higher in the case of unplanted wetland, asserting an accelerated biodegradation rate in the planted case. A difference in the relative concentration of toluene between input and output fluxes at 100 h is found as 13.34% and 30.86% for planted and unplanted wetland setups, respectively. Estimated biodegradation rates show that toluene degradation is 2.5 times faster in the planted wetland setup. In addition, the difference in the observed bacterial count and dissolved oxygen prove that toluene degraded aerobically at a faster rate in the planted setup. Simulations show that as time reached 80–100 h, there is no significant change in concentration profile, thereby confirming the equilibrium condition. The results of this study will be useful to frame plant‐assisted bioremediation techniques for LNAPL‐contaminated soil–water resources in the field.  相似文献   

辽东古元古代镁质非金属矿床成矿系统研究   总被引：4，自引：0，他引：4       下载免费PDF全文

蔡克勤  陈从喜 《地球科学》2000,25(4):346-351

辽东地区古元古代裂谷里尔峪组和大石桥组中分别分布有富镁质的碳酸盐岩建造, 其中产有硼矿、菱镁矿、滑石、岫岩玉等大型-特大型矿床.这些镁质非金属矿床的形成先与古元古代的蒸发岩系有关, 然后经历了吕梁期区域变质和热液交代变质改造, 以及印支、燕山期构造-岩浆作用改造等成矿系统作用过程.其中, 镁质碳酸盐岩建造、成矿构造、成矿流体对镁质非金属矿床的形成起着重要的控制作用.这些矿床也是古元古代矿源场、流体场、热场(能量场)、应力场等在一定的时空条件下耦合和后期构造-岩浆作用叠加改造的综合产物.   相似文献   

探地雷达在大口径基桩无损检测中的应用   总被引：3，自引：0，他引：3  

李梁  兰樟松  张炎孙 《物探与化探》2000,24(6):474-476

介绍了雷达工作原理、检测方法技术。以樟树市某区ZH 11A基桩检测为例,分析了大口径桩的雷达波组特征与桩体结构之间的关系,为探地雷达无损检测大口径桩提供了依据。  相似文献