广义微极近场动力学模型及三维断裂行为模拟

固体断裂破坏是一类非常复杂的现象,一直以来都是工程学科的经典难题。针对准脆性材料的三维断裂问题,提出一种广义微极近场动力学（GMPD）模型。首先,采用Timoshenko梁模拟物质点间的相互作用并建立了相应的控制方程,充分考虑三维条件下键的轴向变形、切向变形和相对转角;其次,引入分别对应键拉伸、剪切和转动刚度的键参数,保证复杂加载条件下近场动力学和传统连续介质力学的能量一致性;同时提出基于能量的新型断裂准则,推导出键轴向变形、切向变形以及相对转角的临界值,可以实现准脆性材料的破坏过程模拟;最后基于所提出的GMPD模型,对轴向压缩条件下准脆性材料的三维断裂过程进行模拟,通过将分析结果与试验结果进行对比,有效验证了本模型的正确性和精度,可以准确描述复杂加载条件下翼型裂纹、反翼型裂纹和次生裂纹等不同类型裂纹的萌生和扩展过程。     

近场动力学理论在钢筋混凝土结构破坏的研究

近场动力学理论(Peridynamic,PD)用键描述了材料内部的相互作用关系,可分析材料破坏过程中的裂纹扩展。针对由异种材料组成的复合材料-钢筋混凝土构建了其力学模型,提出了同种键和异种键,并修正了键的微模量常数、断裂准则等。通过对钢筋混凝土梁的四点弯曲试验进行数值求解,结果表明该力学模型是可行的。     

不同加载条件下混凝土冻融循环能量特征

通过对冻融循环后的多组混凝土试样进行单轴压缩以及3点弯曲强度测定,从损伤和能量的角度分析了不同冻融循环次数下试样的破损特征以及能量耗散的变化特点,并由此分析了冻融环境下混凝土材料的损伤劣化机理.研究表明:单轴压缩试验条件下,试样断裂需要吸收外载做功产生的能量会随着冻融循环次数的增加而逐渐降低;3点弯曲试验条件下,试样断裂需要吸收能量较少,断裂能随着冻融循环次数的增加而显著降低.显著的能量耗散使得混凝土材料逐步损伤并最终形成宏观破裂而强度整体丧失,为深入研究冻融环境下混凝土材料的力学性能和断裂特征奠定了理论基础.     

基于近场动力学方法的结构准静态变形的定量计算

近场动力学(Peridynamics,PD)是一种新兴的基于非局部模型描述材料特性的数值计算方法.该方法假定位于连续体内的粒子通过有限的距离与其他粒子相互作用,通过积分计算在一定近场范围(horizon)内具有一定影响域的材料点之间的相互作用力,而不论位移场的连续与否,避免了传统的局部微分方程求解在面临不连续问题时的奇异性和现有多尺度算法的复杂性.在近场动力学理论框架下,考虑近场范围尺寸对本构力函数的影响,构造了二次多项式型本构力核函数,对反映物质点长程力基本特性的本构力函数进行改进.通过引入人工阻尼、构建分级加载算法和系统失衡判断准则,使近场动力学方法能适用于定量的准静态变形的计算分析.     

弹丸侵彻混凝土靶板破坏过程的近场动力学模拟

为了精确描述弹丸侵彻混凝土靶板的破坏过程及其演化规律,文中采用基于非局部相互作用思想与空间积分方程建模的键型近场动力学(peridynamics,PD)方法,改进了近场动力学本构力核函数,对弹丸侵彻下混凝土靶板的动态破坏过程进行仿真分析。模拟了弹丸侵彻下混凝土靶板破坏的全过程,探讨了不同冲击速度下混凝土靶板的破坏特征,较好地描述了其损伤累积和渐进破坏过程。     

基于内变量热力学的黏弹性本构方程及其基本性质研究

黏弹性变形在沥青混凝土、聚合物等材料中广泛存在,也是岩石材料时效变形的重要组成部分.基于Rice不可逆内变量热力学框架,讨论材料黏弹性变形行为.引入一组内变量表征材料系统内部结构的变化,通过给定余能密度函数和内变量演化方程推导出黏弹性本构方程.方程能包含经典黏弹性模型的本构方程,而且可描述材料的非线性黏弹性变形.对本构方程所基于的基本热力学方程性质进行讨论,表明在约束构型空间中热力学力和内变量之间要满足一定的共轭关系,所建构的本构方程才能刻画材料的黏弹性变形行为;证明了在约束构型空间中流动势函数随时间单调递减;同时指出在统计力学层面流动势函数与表征材料状态的概率密度函数有关.     

爆破荷载作用下岩石破坏特性的“共轭键”基近场动力学数值模拟研究

近场动力学是一种基于非局部弹性理论的积分形式的无网格数值方法.本文为克服传统近场动力学模型中的固定泊松比问题,建立了"共轭键"基近场动力学模型,实现了岩石爆破破坏特性的近场动力学数值模拟.通过引入"共轭键"转动角度及建立微观和宏观变形能的等效关系,推导了"共轭键"基近场动力学模型中的法向刚度参数及切向刚度参数与宏观力学参数之间的关系.另外,通过对影响域中每根"键"所储存的能量密度与临界"键"能量密度进行对比,判断近场动力学模型中的"键"是否断裂,从而实现裂纹起裂、扩展及连接过程的数值模拟.三个数值算例说明:该模型能有效地模拟岩石爆破破坏特性.数值算例与试验结果对比表明,本文所提出的数值方法可以预测岩石材料的爆破破坏模式及特性.     

混凝土裂缝扩展单元能量演变分析

假设材料为黏弹性材料时,带缝混凝土结构在荷载作用下,缝岸相对位移将逐渐增大,如果采用位移直接法计算缝端应力强度因子,该应力强度因子将逐渐增大,甚至可能大于混凝土的断裂韧度。基于信息熵理论对黏弹性材料的断裂问题进行了研究,分析表明,如果结构为黏弹性体,那么结构在流变过程中不涉及到能量的耗散和释放,结构信息熵为一常数,裂缝并不会失稳,即位移直接法不适用于流变断裂问题。对钝裂缝带模型进行了研究,认为裂缝扩展单元开裂时,将引起结构能量的释放,该释放能等于外力功与总弹性应变能的差值,也近似等于裂缝扩展单元开裂前后的总弹性应变能的差值。对于线弹性断裂力学问题,这2个能量差值与裂缝前沿的虚拟扩展长度(平面问题)或虚拟扩展面积(空间问题)的比值,通过简单的转化即可以获得缝端应力强度因子。分析还表明,钝裂缝带模型一定程度上不依赖于网格粗细,且相对分离裂缝模型而言,其剖分网格较方便。     

近场动力学理论在脆性材料破坏研究中的应用现状

近场动力学假定一定范围内的物质点之间存在非局部相互作用,通过空间积分重构物质点的运动方程,克服了传统有限元方法位移场连续性条件的局限,在分析强非线性不连续问题时具有无网格属性的数值优势,已成为研究脆性材料破坏的新兴理论。本文简要介绍了近场动力学的基本内容及其理论框架,总结了近场动力学理论在脆性材料准静态裂纹扩展、动态裂纹扩展及冲击失效研究方面的应用现状。     

近场动力学理论在脆性材料波散射与裂纹扩展问题的数值模拟

近场动力学(Peridynamic,PD)理论是一个物质点具有通用积分运动方程的连续介质理论,其非局部思想能够很好的处理和解决传统连续介质力学在裂纹尖端解的奇异性问题,也弥补了有限元法(FEM)在断裂问题上网格重构的缺陷,在研究材料的断裂与损伤方面有着独特的优势。基于固体力学和断裂力学理论在应力波传播的研究基础上,通过对比传统波动理论和PD理论中P波的传递速度、传递半径及受载出现的波反射和绕射现象,提出近场力波的概念,从本质上分析了近场力波与应力波传递的区别。用PD理论对含预制缺陷的脆性材料(混凝土)动态断裂过程进行数值模拟,通过分析C15混凝土受冲击载荷断裂过程的能量释放速率得出近场力波的传递会对裂纹的萌生和扩展产生影响。     

Characterization of Ordovician carbonate reservoirs, southeastern Saskatchewan, Canada

The discovery of the prolific Ordovician Red River reservoirs in 1995 in southeastern Saskatchewan was the catalyst for extensive exploration activity which resulted in the discovery of more than 15 new Red River pools. The best yields of Red River production to date have been from dolomite reservoirs. Understanding the processes of dolomitization is, therefore, crucial for the prediction of the connectivity, spatial distribution and heterogeneity of dolomite reservoirs.The Red River reservoirs in the Midale area consist of 3～4 thin dolomitized zones, with a total thickness of about 20 m, which occur at the top of the Yeoman Formation. Two types of replacement dolomite were recognized in the Red River reservoir: dolomitized burrow infills and dolomitized host matrix. The spatial distribution of dolomite suggests that burrowing organisms played an important role in facilitating the fluid flow in the backfilled sediments. This resulted in penecontemporaneous dolomitization of burrow infills by normal seawater. The dolomite in the host matrix is interpreted as having occurred at shallow burial by evaporitic seawater during precipitation of Lake Almar anhydrite that immediately overlies the Yeoman Formation. However, the low δ18O values of dolomited burrow infills (-5.9‰～ -7.8‰, PDB) and matrix dolomites (-6.6‰～ -8.1‰, avg. -7.4‰ PDB) compared to the estimated values for the late Ordovician marine dolomite could be attributed to modification and alteration of dolomite at higher temperatures during deeper burial, which could also be responsible for its 87Sr/86Sr ratios (0.7084～0.7088) that are higher than suggested for the late Ordovician seawaters (0.7078～0.7080). The trace amounts of saddle dolomite cement in the Red River carbonates are probably related to "cannibalization" of earlier replacement dolomite during the chemical compaction.     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

A computer generator for randomly layered structures

AcomputergeneratorforrandomlylayeredstructuresYUJia shun1,2,HEZhen hua2(1.TheInstituteofGeologicalandNuclearSciences,NewZealand;2.StateKeyLaboratoryofOilandGasReservoirGeologyandExploitation,ChengduUniversityofTechnology,China)Abstract:Analgorithmisintrod…     

海南岛地体及其毗邻陆缘晚中生代—新生代古地磁研究和构造演化

本文叙述了对海南岛及其毗邻大陆边缘白垩纪到第四纪地层岩石进行古地磁研究的全部工作过程。通过分析岩石中剩余磁矢量的磁偏角及磁倾角的变化,提出海南岛白垩纪以来经历的构造演化模式如下:早期伴随顺时针旋转而向南迁移,后期伴随逆时针转动并向北运移。联系该地区及邻区的地质、地球物理资料,对海南岛上述的构造地体运动提出以下认识:北部湾内早期有一拉张作用,主要是该作用使湾内地壳显著伸长减薄,形成北部湾盆地。从而导致了海南岛的早期构造运动,而海南岛后期的构造运动则主要是受南海海底扩张的影响。海南地体运动规律的阐明对于了解北部湾油气盆地的形成演化有重要的理论和实际意义。     

Exciton Seebeck in Molecular Systems

Various applications relevant to the exciton dynamics,such as the organic solar cell,the large-area organic light-emitting diodes and the thermoelectricity,are operating under temperature gradient.The potential abnormal behavior of the exicton dynamics driven by the temperature difference may affect the efficiency and performance of the corresponding devices.In the above situations,the exciton dynamics under temperature difference is mixed with     

Achieving Unusual States of Matter Under High Pressure

The elongation method,originally proposed by Imamura was further developed for many years in our group.As a method towards O(N)with high efficiency and high accuracy for any dimensional systems.This treatment designed for one-dimensional(ID)polymers is now available for three-dimensional(3D)systems,but geometry optimization is now possible only for 1D-systems.As an approach toward post-Hartree-Fock,it was also extended to     

《Chinese Science Bulletin》SUBJECT INDEX TO VOLUME 59(2014)

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An on-line scaling method for improving scalability of a database cluster

The explosive growth of the Internet and database applications has driven database to be more scalable and available, and able to support on-line scaling without interrupting service. To support more client's queries without downtime and degrading the response time, more nodes have to be scaled up while the database is running. This paper presents the overview of scalable and available database that satisfies the above characteristics. And we propose a novel on-line scaling method. Our method improves the existing on-line scaling method for fast response time and higher throughputs. Our proposed method reduces unnecessary network use, i.e. , we decrease the number of data copy by reusing the backup data. Also, our on-line scaling operation can be processed parallel by selecting adequate nodes as new node. Our performance study shows that our method results in significant reduction in data copy time.     

An improved R-tree based on childnode''s probability

R-Tree is a good structure for spatial searching. But in this indexing structure,either the sequence of nodes in the same level or sequence of traveling these nodes when queries are made is random. Since the possibility that the object appears in different MBR which have the same parents node is different, if we make the subnode who has the most possibility be traveled first, the time cost will be decreased in most of the cases. In some case, the possibility of a point belong to a rectangle will shows direct proportion with the size of the rectangle. But this conclusion is based on an assumption that the objects are symmetrically distributing in the area and this assumption is not always coming into existence. Now we found a more direct parameter to scale the possibility and made a little change on the structure of R-tree, to increase the possibility of founding the satisfying answer in the front sub trees. We names this structure probability based arranged R-tree (PBAR-tree).     

Integrating GIS Web services based on mediating architecture

The geographic information service is enabled by the advancements in general Web service technology and the focused efforts of the OGC in defining XML-based Web GIS service. Based on these models, this paper addresses the issue of services chaining,the process of combining or pipelining results from several interoperable GIS Web Services to create a customized solution. This paper presents a mediated chaining architecture in which a specific service takes responsibility for performing the process that describes a service chain. We designed the Spatial Information Process Language (SIPL) for dynamic modeling and describing the service chain, also a prototype of the Spatial Information Process Execution Engine (SIPEE) is implemented for executing processes written in SIPL. Discussion of measures to improve the functionality and performance of such system will be included.