Unified displacement boundary constraint formulation for discontinuous deformation analysis (DDA)     

David M. Doolin 《国际地质力学数值与分析法杂志》2005,29(12):1199-1207

Displacement boundary constraints in discontinuous deformation analysis (DDA) are applied using stiff penalty springs. A co‐ordinate‐free formulation for displacement boundary constraints is presented here for DDA, which unifies previous derivations for points of fixity, and for points constrained to induce or prohibit block motion in specified directions as a function of location or time. Examples for each type of constraint are used to illustrate the behaviour of the algorithm and provide a link with previous formulations for each case. The new, unified formulation has five benefits: (1) simple to express algorithmically; (2) easy to program and verify; (3) penalty values in different directions may be chosen to allow fixed points, lines, curves or planes; (4) formulation works for 2D and 3D; (5) displacement constraint may be a function of time or location or both. Feedback in the algorithm may induce internal resonance in homogeneously deformable discrete elements used in DDA, and resonance in block‐to‐block contact interactions. Consequently, high mass problems with insufficient damping may suffer from excessive ‘vibrational hammering’, inducing physically implausible behaviour such as elastic rebound. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

Persistence of Summer Sea Surface Temperature Anomalies in the Midlatitude North Pacific and Its Interdecadal Variability     

Xia ZHAO  Guang YANG  Jing WANG 《大气科学进展》2018,35(7):868-880

The present study investigates the persistence of summer sea surface temperature anomalies(SSTAs) in the midlatitude North Pacific and its interdecadal variability. Summer SSTAs can persist for a long time(approximately 8–14 months)around the Kuroshio Extension(KE) region. This long persistence may be strongly related to atmospheric forcing because the mixed layer is too shallow in the summer to be influenced by the anomalies at depths in the ocean. Changes in atmospheric circulation, latent heat flux, and longwave radiation flux all contribute to the long persistence of summer SSTAs. Among these factors, the longwave radiation flux has a dominant influence. The effects of sensible heat flux and shortwave radiation flux anomalies are not significant. The persistence of summer SSTAs displays pronounced interdecadal variability around the KE region, and the variability is very weak during 1950–82 but becomes stronger during 1983–2016. The changes in atmospheric circulation, latent heat flux, and longwave radiation flux are also responsible for this interdecadal variability because their forcings on the summer SSTAs are sustained for much longer after 1982.  相似文献   

Response of the North Pacific Storm Track Activity in the Cold Season to Multi-scale Oceanic Variations of Kuroshio Extension System: A Statistical Assessment     

Peilong YU  Minghao YANG  Chao ZHANG  Yi LI  Lifeng ZHANG  Shiyao CHEN 《大气科学进展》2023,40(3):514-530

In this paper, a statistical method called Generalized Equilibrium Feedback Analysis(GEFA) is used to investigate the responses of the North Pacific Storm Track(NPST) in the cold season to the multi-scale oceanic variations of the Kuroshio Extension(KE) system, including its large-scale variation, oceanic front meridional shift, and mesoscale eddy activity.Results show that in the cold season from the lower to the upper troposphere, the KE large-scale variation significantly weakens the storm tr...  相似文献   

一种基于占有率反馈的虚拟网络映射算法     

王慕阳  陈立全  王翔  王延松  卢华 《南京气象学院学报》2017,9(1):101-105

网络虚拟化技术通过对物理资源的抽象,可以有效解决现有互联网架构中存在的网络结构僵化、可扩展性差等问题.虚拟网络映射问题是指将用户发送的所有虚网请求映射到底层物理网络中,同时还要满足虚网请求中对各个资源的限制要求（如节点计算能力、链路带宽等）.从节点负载平衡的角度出发,在基于就近原则的虚网映射算法基础上,引入节点负载平衡的反馈机制,引导各个虚网请求更均匀地映射到底层物理网络中.另外,在k短路径算法机制中引入了当前链路资源占有率作为评价参考标准,这样可以尽可能均匀地分散链路压力.同时,在检验链路资源是否满足虚网请求的过程中,由于优先选中的链路资源占有率低,所以算法映射成功率高,映射耗时更短,虚拟网络映射效率得到了有效提高.  相似文献   

FBS-3A型反馈式宽频带地震计的传递函数   总被引：5，自引：1，他引：5       下载免费PDF全文

刘庆伟  庄灿涛  刘慧宁 《地震学报》2001,23(1):79-86

FBS-3A型反馈式宽频带地震计是目前广泛使用的一种地震计．对其传递函数开展相关研究，对仪器的使用、观测数据的分析，以及仪器的设计开发具有十分重要的实际意义．本文运用系统分析方法，从阐明仪器的工作原理入手，详尽地推导了该地震计的传递函数（包括标定过程的传递函数和测量过程的传递函数）；在此基础上，分析了其零、极点在复频域的分布情况，从而提供了将该地震计系统从一个高阶系统简化成为一个二阶系统的依据．此外，还以传递函数为基础，对该地震计的频率特性进行了数学仿真计算.   相似文献   

Transfer function of FBS-3A feedback broadband seismometer     

刘庆伟  庄灿涛  刘慧宁 《地震学报(英文版)》2001,14(1):82-90

IntroductionFBS-3A feedback broadband seismometer is a sensor suitable for digital telemetered seismic network observation, which was developed in a key project among the (Eighth Five-Year Plan( to meet the demand for the development of earthquake and premonitor digital observation experiment system (ZHAO, et al, 1997; ZHUANG, 1995).FBS-3A is quite different from conventional mechanical seismometers because electronic feedback technology is applied to it, as a result the measurement ba…  相似文献   

石窟的地学基础及其分类     

张和纬 《甘肃地质》1997,(Z1):138-141

石窟是一种佛教建筑，以往均从宗教、文化和艺术等方面加以研究，但开凿石窟离不开一定的地质地貌，尤其是岩石条件，因此，石窟与地学，特别是岩石有着密切的关系。着重岩石与石窟的关系探讨石窟的地学基础及其分类，从地学的角度探讨有关石窟的保护问题。  相似文献   

CISK, EVAPORATION-WIND FEEDBACK MECHANISM AND 30-60 DAY OSCILLATIONS IN THE TROPICAL ATMOSPHERE_*     

Zhao Qiang  Fu Zuntao  Chen Jiong  Liu Shikuo 《Acta Meteorologica Sinica》1997,11(2):164-175

A baroclinic semi-geostrophic model with evaporation-wind feedback mechanism(EWFM) and CISK is established,two non-dimensional parameters a and η are introduced to represent EWFM and CISK,respectively.Analytic solutions of the model system are obtained,dynamics analyses and the model atmosphere calculations further confirm that EWFM and CISK are very important physical processes in leading to the low-frequency oscillations in the tropics.  相似文献   

对全国复测水准网平差的几点探讨     

薄志鹏  刘国辉  汪晓庆 《武汉大学学报(信息科学版)》1991,(3)

本文讨论复试水准网平差中的几个实际问题,即平差方法的选择,定权的必要精度和验后估计的必要多余观测数等。通过理论分析与实际试算得出了一些有益的结论。  相似文献   

大尺度降雨异常对地面过程的影响——一类气候反馈机制的初步研究   总被引：4，自引：0，他引：4  

李国平  符淙斌  叶笃正 《大气科学》1991,15(2):23-32

本文以华北地区春季两个多雨年和两个少雨年为例,研究半干旱地区大范围持续性降雨对地面物理过程的影响。 根据地面边界层热通量和辐射通量的参数化公式以及地面水份倾向方程,计算分析了春季降雨异常增多后地面热状况、热量平衡各分量和水文状况的变化,发现降雨异常增多后,地面土壤温度和地面气温明显降低,土壤湿度和地面蒸发潜热明显增大,地面反照率也有所降低。值得指出的是,地面物理状况的变化相对于降雨异常过程有明显的时间上的后延现象,在空间场上有较好的配合关系。  相似文献