剪应力作用下Ⅱ型平行节理扩展模式的分叉研究   总被引：1，自引：0，他引：1  

周小平  王建华  张永兴 《岩土力学》2007,28(4):639-642

利用伪力法考虑了剪应力作用下Ⅱ型平行节理之间的相互作用,提出利用节理的长度和间距之比, ,来确定平行裂纹发生分叉的条件。从理论上研究了2条,3条和任意多条平行节理在剪应力作用下的分叉。对于2条平行节理,当节理的长度和间距之比 大于0.816 497 5时,节理的扩展模式要发生分叉;对于3条平行节理,当节理的长度和间距之比 大于0.717 572 8时,节理的扩展模式要发生分叉;对于无穷多条平行节理,当节理的长度和间距之比 大于0.636 638 5时,节理的扩展模式要发生分叉。计算了2条到150条平行节理的分叉问题,结果表明节理数越大,节理发生分叉时节理的长度和间距之比越小。  相似文献   

北赤道流分岔点与印尼贯穿流的相关分析     

赵云霞  魏泽勋  王永刚  徐腾飞  冯颖 《海洋学报(英文版)》2015,34(9):1-11

Based on monthly mean Simple Ocean Data Assimilation(SODA) products from 1958 to 2007,this study analyzes the seasonal and interannual variability of the North Equatorial Current(NEC) bifurcation latitude and the Indonesian Throughflow(ITF) volume transport. Further,Empirical Mode Decomposition(EMD) method and lag-correlation analysis are employed to reveal the relationships between the NEC bifurcation location,NEC and ITF volume transport and ENSO events. The analysis results of the seasonal variability show that the annual mean location of NEC bifurcation in upper layer occurs at 14.33°N and ITF volume transport has a maximum value in summer,a minimum value in winter and an annual mean transport of 7.75×106 m3/s. The interannual variability analysis indicates that the variability of NEC bifurcation location can be treated as a precursor of El Ni?o. The correlation coefficient between the two reaches the maximum of 0.53 with a time lag of 2 months. The ITF volume transport is positively related with El Ni?o events with a maximum coefficient of 0.60 by 3 months. The NEC bifurcation location is positively correlated with the ITF volume transport with a correlation coefficient of 0.43.  相似文献   

Bifurcation current along the southwest coast of the Kii Peninsula   总被引：1，自引：0，他引：1  

Junichi Takeuchi  Naoto Honda  Yoshitaka Morikawa  Takashi Koike  Yutaka Nagata 《Journal of Oceanography》1998,54(1):45-52

Along the southwest coast of the Kii Peninsula, a bifurcation current is regularly observed. By using ADCP data taken on board the R/V Wakayama of the Wakayama Prefectural Fisheries Experimental Station, characteristics of this bifurcation current are analyzed. The occurrence frequency of the bifurcation current reaches about 70% in the period from 1988 to 1996. The bifurcation point appears to be changeable and occurs almost evenly between Cape Ichie and Cape Shionomisaki. The current divergence in the alongshore direction was also investigated. Positive divergence values dominated in the whole analyzed area, and an onshore current appears to be dominant along the southwest coast of the Kii Peninsula, except in 1990 when the Kuroshio flowed in a large meandering path.  相似文献   

长江口南、北港分汊口演变与治理   总被引：11，自引：0，他引：11  

薛鸿超 《海洋工程》2006,24(1):27-33

按输水输沙特征,中等潮汐长江口多年来保持“三级分汊,四口入海”地貌形态格局。第二级南、北港分汊口问题已成为当今发展重要障碍之一。近百年来南、北港分汊口呈周期性冲淤演变,1971年前后共约10年,中央沙头石头沙西10 km左右的分汊口位置最佳,河势归顺,河床稳定,南、北港都畅通。现今分汊口正处于剧烈变动时期,分汊口治理,南支及其下游河段的开发与工程须认真考虑其影响与对策。  相似文献   

Improved prediction of the threshold of surf-riding of a ship in steep following seas     

Wan Wu  Kostas J. Spyrou 《Ocean Engineering》2010,37(13):1103-1110

An extended version of Melnikov's method is implemented in order to predict more accurately the threshold of global surf-riding for a ship operating in steep following seas. The key advantage of the proposed method is that it overcomes the limitation of small damping and/or small forcing that are intrinsic to the implementation of the standard Melnikov's method. A reference ITTC ship is used here by way of example and the result is compared to that obtained from standard analysis as well as numerical simulations. Because of the primary drawback of the extended Melnikov's method is the inability to arrive at a closed form equation, in this work the authors arrive at a “best fit” approximation to the extended Melnikov numerically predicted result.  相似文献   

Nonlinear Dynamic Behavior of Moored Buoy Excited by Free Surface Waves     

常宗瑜  徐长密  李华军  唐原广  张喜超 《中国海洋工程》2009,23(3):585-592

In this paper, studied are the dynamics of a moored buoy near the surface subjected to wave excitation. According to the physical structure, submersible buoy moored by tethered line is modeled firstly. Then from the differential equations, the natural frequencies are estimated by neglecting the coupling between tangential and normal direction. By use of numerical integration method, solutions are obtained. On this basis, strange attractors and bifurcation phenomena are obtained by applying Poincare map, pha...  相似文献   

变参数赤潮藻类生长模型的非线性动力分析研究     

王洪礼  葛根  许佳  向建平 《海洋通报》2007,26(3):48-52

在对一个营养盐和赤潮藻类摄食模型进行非线性分析的基础上,提出了含有变参数的赤潮藻类生长模型。模型中用一个周期阶跃函数来近似模拟了藻类生长率参数,并对此模型做了数值模拟。结果表明,引入变参数后的模型更能体现藻类生长的季节性特点,和实际情况符合更好。  相似文献   

Micro‐inertia origin of instabilities in granular materials          下载免费PDF全文

Antoine Wautier  Stephane Bonelli  François Nicot 《国际地质力学数值与分析法杂志》2018,42(9):1037-1056

Within the framework of the second‐order work theory, the onset of instabilities is explored numerically in loose granular materials through three‐dimensional DEM simulations. Stress controlled directional analysis are performed in Rendulic's plane, and a particular attention is paid to transient evolutions at the microscale. Thanks to a micromechanical analysis, the onset and development of transient mechanical instabilities is explored. It is shown that these instabilities result from the unjamming and bending of a few force chains associated with a local burst of kinetic energy. This burst of kinetic energy propagates to the whole sample and provokes a generalized unjamming of force chains. As force chains buckle, a phase transition from a quasi‐static to an inertial regime is observed. At the macroscopic scale, this results in a transient softening and a loss of controllability. After the collapse of existing force chains, the development of plastic strain is eventually stopped as new stable force chains are built.  相似文献   

Diffuse bifurcations engraving diverse shear bands in granular materials          下载免费PDF全文

Yuki Yamakawa  Kiyohiro Ikeda  Isao Saiki  Jacques Desrues  Reiko J. Tanaka 《国际地质力学数值与分析法杂志》2018,42(1):3-33

Shear bands with characteristic spatial patterns observed in an experiment for a cubic or parallelepiped specimen of dry dense sand were simulated by numerical bifurcation analysis using the Cam‐clay plasticity model. By incorporating the subloading surface concept into the plasticity model, the model became capable of reproducing hardening/softening and contractive/dilative behavior observed in the experiment. The model was reformulated to be compatible with the multiplicative hyperelasto‐plasticity for finite strains. This enhanced constitutive model was implemented into a finite‐element code reinforced by a stress updating algorithm based on the return‐mapping scheme, and by an efficient numerical procedure to compute critical eigenvectors of elastoplastic tangent stiffness matrix at bifurcation points. The emergence of diamond‐ and column‐like diffuse bifurcation modes breaking uniformity of the materials, followed by the evolution of shear bands through strain localization, was observed in the analysis. In the bifurcation analysis of plane strain compression test, unexpected bifurcation modes, which broke out‐of‐plane uniformity and led to 3‐dimensional diamond‐like patterns, were detected. Diffuse bifurcations, which were difficult to observe by experiments, have thus been found as a catalyst creating diverse shear band patterns.  相似文献   

Thermoplasticity and strain localization in transversely isotropic materials based on anisotropic critical state plasticity          下载免费PDF全文

Shabnam J. Semnani  Joshua A. White  Ronaldo I. Borja 《国际地质力学数值与分析法杂志》2016,40(18):2423-2449

Geomaterials such as soils and rocks are inherently anisotropic and sensitive to temperature changes caused by various internal and external processes. They are also susceptible to strain localization in the form of shear bands when subjected to critical loads. We present a thermoplastic framework for modeling coupled thermomechanical response and for predicting the inception of a shear band in a transversely isotropic material using the general framework of critical state plasticity and the specific framework of an anisotropic modified Cam–Clay model. The formulation incorporates anisotropy in both elastic and plastic responses under the assumption of infinitesimal deformation. The model is first calibrated using experimental data from triaxial tests to demonstrate its capability in capturing anisotropy in the mechanical response. Subsequently, stress‐point simulations of strain localization are carried out under two different conditions, namely, isothermal localization and adiabatic localization. The adiabatic formulation investigates the effect of temperature on localization via thermomechanical coupling. Numerical simulations are presented to demonstrate the important role of anisotropy, hardening, and thermal softening on strain localization inception and orientation. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献