摩擦和非线性对斜压初始扰动发展的影响

通过一个二维非线性斜压Eady波模式,讨论了斜压系统中初始扰动快速发展的动力学机制.由于斜压切变气流存在,其对扰动位涡的平流作用可引起初始扰动位涡的"位涡非屏蔽"(potential vorticity unshielding),导致线性系统初始扰动的快速增长.摩擦作用主要通过耗散局地扰动位涡,改变扰动位涡异常结构,特别是水平方向的位涡异常分布,从而减弱初始扰动位涡的"位涡非屏蔽"作用,抑制系统初始扰动动能的快速增长.非线性作用可以抑制较大振幅扰动的增长,同时引起扰动位涡异常丰富的垂直结构产生,导致初始扰动位涡的"位涡非屏蔽"的减弱,从而抑制初始扰动的快速增长.不同的初始扰动结构,可以产生不同的扰动位涡异常结构,相应存在不同的"位涡非屏蔽"作用,导致初始扰动的快速增长过程不同.位涡异常水平结构为"正负正"或"负正负"分布时,有利于初始扰动的快速增长,而上下层异号的扰动位涡异常在垂直方向间隔的距离越大,越有利于初始扰动的快速发展,这些结果进一步深化了对"位涡非屏蔽"的理解.     

基于物理约束扰动的EnSRF雷达资料同化

在完善WRF集合均方根滤波同化系统的双向嵌套预报方案、雷达资料质量控制方案和多微物理过程积分方案的基础上,引入了一种扰动势函数、流函数的尺度较小、物理意义更明显的集合初始扰动新方案.通过台风“桑美”登陆过程中的多普勒雷达资料直接同化试验,对比新扰动方案与目前应用较多的背景误差协方差随机扰动和全场随机扰动方案,对集合滤波同化效果的影响.试验结果表明,3种初始扰动方案都有效改善了台风内部结构,但新方案由于尺度更小、结构更为合理,其同化效果也更为显著,提高了对台风路径、中心最低气压、最大风速及降水的预报质量.     

Dynamic response of double beam rested on stochastic foundation under harmonic moving load

This paper deals with the dynamic response of infinite double Euler–Bernoulli beam supported by elastic foundation with stochastic stiffness subjected to an oscillating moving load, which is the first research in relevant literature review. In this matter, equations of motion for double beam are formulated in a moving frame of reference. Moreover, by employing the first order perturbation theory and calculating contour integration, the response of double beam is obtained analytically and validated by a stochastic finite element model. Sensitivity analyses on the various parameters of closed form solution such as velocity, load frequency, coefficient of variation of soil foundation and rail and slab bending stiffness show the significant effect of load frequency on the dynamic response of the doubled beam. From practical point of view, the obtained results of the present study can be utilized efficiently in analysis and design of slab track systems. Copyright © 2013 John Wiley & Sons, Ltd.     

A simple analytical solution to one‐dimensional consolidation for unsaturated soils

This paper presents a simple analytical solution to Fredlund and Hasan's one‐dimensional (1‐D) consolidation theory for unsaturated soils. The coefficients of permeability and volume change for unsaturated soils are assumed to remain constant throughout the consolidation process. The mathematical expression of the present solution is much simpler compared with the previous available solutions in the literature. Two new variables are introduced to transform the two coupled governing equations of pore‐water and pore‐air pressures into an equivalent set of partial differential equations, which are easily solved with standard mathematical formulas. It is shown that the present analytical solution can be degenerated into that of Terzaghi consolidation for fully saturated condition. The analytical solutions to 1‐D consolidation of an unsaturated soil subjected to instantaneous loading, ramp loading, and exponential loading, for different drainage conditions and initial pore pressure conditions, are summarized in tables for ease of use by practical engineers. In the case studies, the analytical results show good agreement with the available analytical solution in the literature. The consolidation behaviors of unsaturated soils are investigated. The average degree of consolidation at different loading patterns and drainage conditions is presented. The pore‐water pressure isochrones for two different drainage conditions and three initial pore pressure distributions are presented and discussed. Copyright © 2013 John Wiley & Sons, Ltd.     

Response of a Grassland Ecosystem to Climate Change in a Theoretical Model

The response of a grassland ecosystem to climate change is discussed within the context of a theoretical model.An optimization approach,a conditional nonlinear optimal perturbation related to parameter(CNOP-P) approach,was employed in this study.The CNOP-P,a perturbation of moisture index in the theoretical model,represents a nonlinear climate perturbation.Two kinds of linear climate perturbations were also used to study the response of the grassland ecosystem to different types of climate changes.The results show that the extent of grassland ecosystem variation caused by the CNOP-P-type climate change is greater than that caused by the two linear types of climate change.In addition,the grassland ecosystem affected by the CNOP-P-type climate change evolved into a desert ecosystem,and the two linear types of climate changes failed within a specific amplitude range when the moisture index recovered to its reference state.Therefore,the grassland ecosystem response to climate change was nonlinear.This study yielded similar results for a desert ecosystem seeded with both living and wilted biomass litter.The quantitative analysis performed in this study also accounted for the role of soil moisture in the root zone and the shading effect of wilted biomass on the grassland ecosystem through nonlinear interactions between soil and vegetation.The results of this study imply that the CNOP-P approach is a potentially effective tool for assessing the impact of nonlinear climate change on grassland ecosystems.     

局地大气能量有效性中的表面扰动位能特征

在局地扰动位能理论工作基础上,进一步研究了与实际地形有关的表面扰动位能部分,理论推导了数学表达式,表明地形和表面热状况是其决定因素。利用再分析资料考察了其气候学和气候变率特征。研究表明,表面扰动位能具有独特的热动力学意义,它的量值与地球表面高大地形密切联系,而其季节变动特点则与表面热状况的季节变化息息相关。高纬度极地地形区域为明显的全年基本不变的负扰动位能分布区,低纬度热带区域则呈现季节变动非常小的正扰动位能分布。表面扰动位能的季节变动和年际变率的极值区都位于北半球中纬度的高大地形区域,夏季达到正的极大值,而冬季则转变成负值区。这一特征在青藏高原区最为典型,其表面扰动位能在时域和频域上均表现出明显的年代际特征,年际变率以2—4a周期为主。     

RegCM3对中国区域气候模拟的敏感性试验

为使区域气候模式RegCM3在中国区域气候的模拟中取得更好的模拟效果,针对RegCM3进行了初始场、模式水平分辨率、侧边界方案及积云对流方案的敏感性试验.结果表明:①从冬季开始的积分,模拟结果对初始场的依赖性较小;②模式水平分辨率的提高不一定会带来模拟效果的显著改善,高分辨率的嵌套模拟会对模拟效果有一定程度的改善;③选...     

紫坪铺水库与汶川地震关系的讨论

利用紫坪铺水库专用地震台站和加密地震台站资料,使用双差法完成了震前930次地震、汶川8级主震和5, 789次余震的重新定位,探讨了紫坪铺水库与汶川地震之间的关系,获得了有利于证明它们之间密切关联的事实: 1)紫坪铺水库2005年蓄水之后出现了水磨、深溪沟和都江堰震群,地震应变能释放增加了200%,与库水位变化密切相关,在汶川地震前呈现出加速释放的现象; 2)野外调查表明存在1条贯穿紫坪铺水库库区、走向NE的同震地表破裂带,与中滩铺断层位置一致; 3)余震分布以中滩铺断层为界,西北上盘多,东南下盘少; 4)利用P波初始到时重新确定出的汶川主震发震时刻为27分59.5秒,初始破裂深度在6～9km左右,直接位于水磨震群之下; 5)汶川主震与发生在2008年4月5日水磨震群中的1次小震的各个台站到时差相同。     

静动应力作用下大连饱和黏土的剪切特性研究

针对人工制备的大连饱和黏土,在静应力与循环应力联合作用下进行了多组循环剪切试验,着重探讨了初始静力大小及加载速率对循环剪切变形特性的影响.试验表明静应力与循环应力作用下饱和黏土具有循环蠕变特性,总应变由初始静应变和循环蠕变两部分组成,其中循环蠕变主要受循环应力幅值、初始静应力大小及其加载速率的影响,循环蠕变的逐次增加量...     

STRATA反演技术及其在YK地区解释砂体的应用

地震波阻抗反演技术是国内、外油气储层预测的关键技术之一。针对YK三维工区目的层砂体薄、横向变化快的特点,运用STRATA反演技术对其进行砂体预测。这里论述了STRA-TA反演的基本原理,实现流程,关键环节,以及在实际工区的运用。通过对反演结果的分析,明确了砂体的空间分布范围以及砂体的厚度,并做出了砂体视厚度平面分布图,对进一步勘探开发提供了明确的目标。