悬臂输流单层碳纳米管的颤振失稳分析

基于非局部弹性理论及欧拉-伯努利梁模型,并考虑了碳纳米管材料的黏弹性以及小尺度效应,应用哈密顿原理建立了悬臂输流单层碳纳米管(SWCNT)的振动方程以及边界条件,借助微分变换法(DTM)对此高阶偏微分方程进行求解,通过数值计算研究了管内流体流速、小尺度参数、质量参数和黏弹性参数对悬臂输流单层碳纳米管动力学行为的影响。结果表明,小尺度参数的增加将会降低悬臂输流系统的稳定性,使系统更为柔软;悬臂输流系统颤振失稳临界流速的大小是由管道自流体中的吸入能、管道系统储存的弹性能以及管道黏弹性特性的振动耗散能三者共同决定的。     

部分浸入水中弹性支承Timoshenko梁动力特性

研究了部分浸入流体中自由端具有集中质量块的等截面弹性支承Timoshenko悬臂梁横向振动的固有频率和振型特征.考虑梁横截面转动和剪切变形以及集中质量块引起轴向压力的影响,建立了支承处弹性水平位移约束和转动约束耦合情形下悬臂梁横向自由振动的数学模型.由于集中质量块的惯性力和惯性矩,此模型的边界条件与振动频率相关.推导了Timoshenko梁的频率方程和振动模态的广义正交条件.数值研究了集中质量块质量、转动惯量、质心距以及弹簧刚度系数等参数对Timoshenko悬臂梁固有频率的影响.数值结果表明：由于横截面转动和剪切变形效应的影响,相比于Euler-Bernoulli梁模型,Timoshenko梁的固有频率减小,对高阶频率的影响尤为显著;弹簧刚度耦合项的增大将减小梁的固有频率;轴向力的增加将减小梁的低阶固有频率,但对高阶固有频率的影响不大.     

磁场下黏弹性基中输流纳米管的颤振失稳分析

基于非局部欧拉-伯努利梁模型，研究了外部轴向磁场作用下黏弹性基体中悬臂输流单层碳纳米管系统的动态失稳特性。黏弹性基体采用线性Kelvin-Voigt弹性基模型，利用哈密顿原理，建立该系统的振动微分方程及其边界条件。应用微分变换法求解该振动方程，着重研究不同质量比下，黏弹性基体、轴向磁场与小尺度效应共同影响时，该系统的颤振失稳特性。数值计算结果表明：黏弹性基体的弹性参数与外加轴向磁场的增加均能提高悬臂输流碳纳米管系统的稳定性，而小尺度系数的增加则降低系统稳定性。不同质量比下，黏弹性基体的阻尼系数对系统动态稳定性的影响不同。进一步研究表明，随着轴向磁场与基体弹性参数的共同增加，系统稳定性的提升并未呈现“协力效应”，而是各自的提升效果均有所减弱。     

黏弹性地基上欧拉梁的横向自由振动

研究了黏弹性三参数地基上有限长欧拉梁的横向自由振动.给出了简支边界条件下的频率方程和模态方程,进而推导出模型地基梁的固有频率和模态函数的解析表达式,提供了精确计算任意一阶频率和模态的简便方法.在具体算例中,运用推导出的公式能方便地计算出低阶和高阶频率的精确值,避免了以往数值方法带来的计算误差.同时通过具体算例分析了不同物理参数对黏弹性地基上欧拉梁的振动特性的影响.     

纵向磁场中载流单层碳纳米管的振动与失稳

以非局部弹性理论为基础,采用Euler-Bernoulli梁模型,并考虑纳米管管形区域内滑移边界条件以及小尺度效应,研究了纵向磁场中单层载流碳纳米管的振动与失稳问题。根据哈密顿原理获得碳纳米管的横向振动方程和边界条件。应用微分变换法(DTM)对此高阶偏微分方程进行求解,通过数值计算分析磁场强度、小尺度参数和Knudsen数对单层载流碳纳米管振动频率和稳定性的影响。结果表明,小尺度参数和Knudsen数越大,系统基频及临界流速就越低,系统的稳定区域也越小;纵向磁场强度增加到一定程度后,磁场作用将明显提高系统的基频及临界流速,也即增大了系统的稳定区域。     

多重边界约束对三壁碳纳米管振动特性的影响

主要研究了三壁碳纳米管在多重边界约束条件下的振动特性. 基于Euler 梁模型将三壁碳纳米管模拟成三重相合梁系统, 其中管间通过范德华力 (van der Waals force) 相合, 但内管、中管、外管处于不同的边界约束中, 并研究了FFC (free-free-clamped) 型多重边界约束对 三壁碳纳米管振动的影响. 结果表明, FFC 型多重边界约束会导致三壁碳纳米管共振频率的降低, 尤其在低阶振动模态上; 同时, 这种影响会随着碳纳米管长度的增加而减弱.     

基于有限元法的数控车床主轴系统频率可靠性分析

基于有限元法参数化建立主轴系统三维有限元模型,将轴承简化为弹性支撑.考虑皮带轮和卡盘的影响,对整个主轴系统进行模态分析,得到主轴系统的前八阶固有频率及固有振型.进行临界转速分析,将工作转速与非零最低阶频率对应的转速进行比较,验证主轴设计的合理性.利用ISIGHT集成ANSYS进行正交试验设计并计算非零最低阶固有频率,将有公差范围要求的轴段的直径和长度以及基本物理参数作为随机变量,采用BP神经网络拟合主轴系统非零最低阶固有频率与随机变量之间的关系.利用一次二阶矩法计算主轴系统在特定转速下的可靠度并求解各随机参数的可靠性灵敏度.     

不同约束条件下风机塔筒扭转自由振动特性分析

针对风力发电机组(以下简称风机)的自由扭转振动,建立了非均质变截面风机塔筒模型。采用微分求积法计算了风机塔筒扭转振动在不同边界下的无量纲固有频率,求解并分析了弹性地基对风机塔筒扭转无量纲固有频率的影响,同时给出了弹性地基上风机塔筒扭转振动前六阶振型。引入并分析了质量变化系数、切变模量变化系数和截面变化系数对风机扭转振动无量纲固有频率的影响。结果表明微分求积法求解精度较高,计算量小;风机塔筒扭转无量纲固有频率随质量变化系数增大而增大、随切变模量变化系数增大而减小,且质量变化系数和切变模量变化系数均对高阶频率影响较大,对前二阶频率影响较小;截面变化系数仅影响风机塔筒扭转前二阶无量纲固有频率,对高阶固有频率影响甚微。     

轴向力作用下弹性支承连续梁的固有横振

采用整体分析和拉普拉斯变换方法,研究了轴向力作用下考虑支承质量时弹性支承多跨均匀连续梁的横向振动,推导出了频率方程和振型函数的解析表达式．所得公式全面、完整,适用于各种中间支承情况和各种轴向力情况．通过实例分析了支承质量和支承弹簧刚度对连续梁固有频率的影响．结果表明,支承质量会降低连续梁的固有频率,但对低阶固有频率的影响很小．特别是当支承质量较小时,完全可以不考虑其对低阶固有频率的影响．连续梁固有频率随着支承弹簧刚度的增大而增大,当弹簧刚度很大时,弹性支承连续梁的固有频率接近于刚性支承连续梁的固有频率．     

考虑频变特性的约束阻尼结构建模与试验研究

为了提高黏弹性约束阻尼结构模型仿真精度,提出一种考虑频变特性的约束阻尼结构建模方法,并开展了试验验证.首先,对ZN-3黏弹性材料进行动态试验测试,基于最小二乘法获取黏弹性材料模量和损耗因子表达式;其次,根据ZN-3黏弹性材料损耗因子关系表达式,基于考虑频变特性的修正模态应变能法,求解了约束阻尼结构的固有频率和模态损耗因子;最后,以贴敷黏弹性阻尼材料的悬臂约束阻尼薄板为例,从理论与试验两方面校验,结果表明,考虑频变特性的约束阻尼结构有限元模型具有较高精度,与试验测试结果比较误差在5%以内,验证了建模方法的准确性.     

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.     

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.     

Tracking data management using topology of moving object database system for moving object constrained trajectory in LBS application

Advances in wireless technologies and positioning technologies and spread of wireless devices, an interest in LBS (Location Based Service) is arising. To provide location based service, tracking data should have been stored in moving object database management system (called MODBMS) with proper policies and managed efficiently. So the methods which acquire the location information at regular time intervals then, store and manage have been studied. In this paper, we suggest tracking data management techniques using topology that is corresponding to the moving path of moving object. In our techniques, we update the MODBMS when moving object arrived at a street intersection or a curved road which is represented as the node in topology and predict the location at past and future with attribute of topology and linear function. In this technique, location data that are corresponding to the node in topology are stored, thus reduce the number of update and amount of data. Also in case predicting the location,because topology are used as well as existing location information, accuracy for prediction is increased than applying linear function or spline function.