A time-based arc-length like method to remove step size effects during fracture propagation

An arc-length like method is presented which alters the size of the time increment when simulating crack propagation problems. By allowing the time increment to change during the time step a constraint can be imposed, which is used to enforce the fracture to propagate a single element length per time step. This removes the effect of the (interface) element size on propagating fractures, and therefore allows smooth fracture propagation during the simulation. The benefits of the scheme are demonstrated for three cases: mode-I crack propagation in a double cantilever beam, a shear fracture including inertial and viscoplastic effects in the surrounding material, and a pressurized fracture inside a poroelastic material. These cases highlight the ability of this scheme to obtain more accurate and nonoscillatory results for the force–displacement relation, to remove numerically induced stepwise fracture propagation, and to allow for arbitrary propagation velocities. An added benefit is that plastic strains surrounding a fracture are no longer affected by the (interface) element size.     

Growth and Life History Patterns of a Small‐bodied Stream Fish,Cottus cognatus,in Hydropeaking and Natural Rivers of Northern Ontario

Hydroelectric facilities can dramatically alter the quantity and quality of fish habitat; however it is not well known how these habitat changes affect the growth and life history of fish. We examine the growth and life history of slimy sculpin (Cottus cognatus), a small‐bodied sedentary, benthic stream fish, in two regulated and eight unregulated tributaries of Lake Superior, Canada. Among rivers, we found that slimy sculpin grew faster in the regulated Magpie River than in nearby unregulated systems, whereas growth in the Michipicoten River was intermediate. Sculpin were also in better condition in the regulated Magpie and Michipicoten than in nearby natural rivers. Faster growth of sculpin, however, potentially led to their rapid maturity and higher instantaneous mortality in regulated rivers. Within the regulated rivers, there are strong longitudinal gradients in growth, with sculpin at sampling sites near the dams growing more rapidly, maturing earlier and attaining a larger size‐at‐age than sculpin at sites farther downstream or in natural systems. Differences in sculpin life history traits within rivers closely followed spatial patterns in food availability. We caution future researchers and managers to acknowledge the longitudinal gradients in abiotic and biotic conditions below dams early in experimental designs and monitoring programmes and how this may impact the measures of central tendency and statistical power when comparing rivers. Copyright © 2015 John Wiley & Sons, Ltd.     

拉伸载荷作用下无限大板中三角孔-裂纹问题

针对Bueckner原理普遍化,提出了一种求解远方载荷作用下无限大板中孔边裂纹问题的数值方法.通过把适于单一裂纹的Bueckner原理扩充到远方载荷作用下无限大板中孔边裂纹问题,将原问题分解为承受远方载荷不含孔边裂纹的均匀问题和在远方不承受载荷但在裂纹面上和孔的表面上承受面力的问题.算例说明本数值方法对分析无限大板中孔...     

裂纹对悬臂梁力学响应影响的扩展有限元模拟

扩展有限元继承了传统有限元的优点,在求解以裂纹扩展等为代表的一类不连续力学问题时具有明显的优势.主要探讨了含裂纹单元的积分域剖分,应用Fortran语言开发了相应的程序代码.以悬臂梁结构为例探讨了裂纹以及裂纹扩展对其力学响应的影响,数值结果表明了程序开发的正确性.     

岩体结构面模拟方法探析

结合盐津桥水库右岸岩体结构面的实际情况,综合考虑结构面的几何特征和力学特征,针对不同类型的结构面,先运用蒙特卡洛（Monte-Carlo）方法获得随机结构面的几何参数,再利用有限元软件ANSYS对确定性结构面进行数值模拟,以获得有效的结构面模拟方法。此方法有效地解决了难以对数量多、尺寸小的随机节理进行逐条模拟的问题,又从变形和强度的弱化方面把节理考虑进去,与现实情况近似,是一种行之有效的方法。     

微带线不连续性对光电导开关非线性特性的影响

实验对自行研制的全固态同轴―微带型横向半绝缘砷化镓(SI-GaAs)光电导开关传输特性进行了研究：当偏置电压达到一定阈值时,普通开关进入了非线性锁定（Lock-on）工作模式;在相同实验条件下,当微带线出现不连续时,输出的电脉冲波形没有出现锁定现象;分别用空气击穿的流注模型和微带线等效电容机理分析了微带线不连续效应引起整个开关电路性能变化及抑制开关Lock-on效应的原因。     

非连续裂隙岩体渗流场与温度场耦合分析

在岩体水力学研究中,一个重要的问题就是岩体渗流场与温度场的耦合分析。笔者关注了国内外相关的研究,对其发展的趋势进行了展望,认为目前有关非连续性裂隙岩体渗流场与温度场的耦合分析研究相对很少,并给出了拟研究的内容和方法。     

一种基于结构面密度的岩体结构均质区划分方法

根据结构面发育的主要特点以及工程实际需要，合理选择划分岩体结构均质区的岩体参数是必要的。在某些特殊情况下，选择结构面密度作为划分均质区的依据更为合适。为此，提出了一种基于结构面密度的岩体结构均质区划分方法，即密度分区方法，并通过对西南某大型水电站工程侧裂结构面的密度分区，证明了该方法的可行性。该方法简单、直观、易于操作，有很强的推广实用价值。     

岩质边坡结构面抗剪强度参数的实用确定方法研究

对坡高不大、坡体量较小的中小岩质边坡,由于资金和技术条件所限,目前确定岩体结构面抗剪强度参数大多来自规范和经验,边坡处治往往很难兼顾安全性和经济性。本文对15~30m高岩质边坡中控稳结构面抗剪强度参数粘聚力c、内摩擦角在边坡稳定中各自发挥的作用进行了定量分析。研究表明:当坡高小于25m时,抗剪强度参数中c值是边坡稳定的主要控制因素,因而提出采用现场原位抗切试验确定c值,再结合规范取值确定值。这种方法通过现场实测确定了主要参数,同时克服了做大型原位剪切试验时间长和费用高的缺点,是一种经济、实用的边坡结构面抗剪强度参数确定方法。     

岩体结构面抗剪强度参数试验研究

从工程实际出发,讨论了岩体结构面直剪试验方法的选取原则。工程实例表明,采用现场原位抗切试验确定结构面c值,再结合规范取值确定φ的方法更适用于坡高小于25m的中小岩质边坡。结合乌江构皮滩水电站岩体结构面大型原位抗剪试验成果,分析了结构面性状对结构面抗剪强度的影响。本文还通过多组室内试验研究了水对结构面抗剪强度的弱化作用,得出若干有益的结论。