地铁线路轨距对轮轨接触行为的影响

为揭示地铁线路轨距对轮轨接触特性的影响,基于轮轨接触几何关系、Kalker三维非Hertz弹性体滚动接触理论及其数值程序CONTACT,利用我国地铁车辆常用的LM型面与CHN60钢轨,计算轨距对轮轨接触几何参数和力学特性的影响。研究结果表明:轨距加宽引起相同横移量下轮轨接触点偏向钢轨中心位置;轮轨接触滚动圆半径和接触角减小,增大了滚动圆半径和接触角剧增的横移量,导致轮缘不易产生贴靠;与标准轨距相比,轨距变窄引起轮轨接触斑横向分布变窄,纵向分布变宽,接触斑面积减小;轨距加宽至1 437 mm后接触斑开始出现黏着区,加宽至1 439 mm时接触斑内黏着区面积显著增大,其接触斑面积增大77%,减小轮轨的滑动行为;轨距在1 433～1 439 mm之间变化,轮轨接触斑内正应力和切应力显著降低,轮轨体内最大等效应力显著减小,且等效应力沿纵向分布范围变宽,沿深度方向影响范围增大,可避免等效应力的集中作用。轨距加宽有利于地铁线路轮轨关系的匹配,减轻轮轨间的磨耗和疲劳伤损。     

高速轮轨瞬态滚动接触行为的研究

该研究建立了三维瞬态滚动接触有限元模型,用于求解速度高至500 km/h的轮轨瞬态滚动接触行为。该模型考虑了轮轨的真实几何形状,可引入任意接触面不平顺、黏着系数(或摩擦系数)沿钢轨纵向的波动及相对滑移速度对黏着系数的影响,并可考虑材料的非线性行为。不同的切向接触载荷,即不同运动状态下的车轮所承受的驱动或制动力,由施加于车轴的随时间变化的扭矩来控制。模型采用显式有限元方法,其条件稳定特性决定了计算时间步长需取值极小,这使得该模型适合于时域内求解轮轨高速滚动过程中的高频动态或瞬态现象,如分析轮轨接触表面短波长缺陷处(钢轨焊接接头、波浪形磨损和车轮扁疤等)的轮轨瞬态冲击响应。另外,模型中充分考虑了车辆转向架和轨道子系统的主要部件,数值重现了三维轮对的真实滚动行为,因此车辆—轨道的耦合作用、与高速滚动相关的自旋、陀螺仪效应等因素均包含于模型之中。过去一年多,应用上述三维高速瞬态滚动接触有限元模型进行了一系列研究。不同速度的模拟结果发现,500 km/h以下速度对光滑接触表面上压力分布的影响可以忽略,而相应的应变率随速度增加而增加。针对很多国家出现的钢轨表面塌陷现象,即钢轨接触带内出现的具有两瓣特征且第二瓣更大的局部滚动接触疲劳损伤,也进行模拟研究,结果显示其发生应该与轨下胶垫的刚度有很大关系。车轮滚过钢轨短波波磨的瞬态接触结果显示,轮轨接触力在波磨段呈现出明显的波动,且当波深足够深时,接触状态会在滚滑—滑动—滚滑间反复震荡,从而导致V-M应力与摩擦功的波动。跟传统的基于多体动力学的车辆—轨道耦合动力学结果相比,发现传统模型夸大了轮轨间的接触刚度。另外,随相对滑动速度变化的摩擦力模型被发现对轮轨间的切向滚动接触具有重要的影响。     

轨枕空吊动态演变规律

在车辆-轨道耦合系统动力学模型和道床沉降模型的基础上,提出了一种基于迭代计算的预测方法,对轨枕局部空吊后的动态演变过程进行了合理的预测.结果表明:当轨枕单侧轨底处出现局部空吊时,空吊区域的承载力明显降低,而与之相邻区域承受的车辆载荷增加,导致相邻区域轨枕空吊间隙发展较快,从而形成空吊区域由轨枕两端轨底处向轨枕中心扩展的动态演变过程;随着轨枕空吊区域的不断扩大,整根轨枕的承载力大幅降低,大部分列车载荷主要由相邻未出现空吊的轨枕承担,因而轨枕的空吊发展程度逐渐趋于平缓,最终大部分区域存在1.5 mm左右的空吊间隙.     

轨枕空吊对桥上有砟轨道结构动力响应的影响

基于车辆-轨道耦合动力学理论,将轨枕下部的有砟轨道考虑为弹簧-阻尼系统,假设该弹簧-阻尼系统失效来模拟轨枕空吊状态,建立含轨枕空吊的有砟轨道-桥梁耦合模型.采用Newmark直接积分法求解车辆-轨道-桥梁耦合动力学方程,计算列车通过时轨枕正常状态和空吊状态下轨道结构的位移和加速度,同时对空吊轨枕出现的数量及纵向分布位置对轨道结构动力特性的影响进行分析.对轨枕无空吊状态、单根空吊状态、连续2根空吊和间隔2根轨枕空吊4种工况下轨道结构的动力响应进行分析.研究结果表明:连续2根轨枕空吊影响下轨道响应显著大于其他3种工况,间隔2根轨枕空吊的影响略大于单根轨枕空吊的影响,但差别较小;轨枕空吊对有砟轨道结构动力影响范围沿轨道纵向不超过2跨轨枕间距;随着列车运行速度的增加,轨枕空吊影响下轨道结构位移变化较小,加速度则明显加大,基本呈线性增长.     

基于瞬态接触特性的科隆蛋扣件轨道波磨形成机理

为从轮轨瞬态接触黏滑振动角度探究地铁线路上钢轨波磨的形成机理,该文首先根据现场波磨情况建立了三维轮轨滚动接触有限元模型并论证其有效性;然后,分析了车轮运行过程中的接触黏滑状态,并讨论了轮轨接触黏滑特性与波磨生成的关系;最后,研究了轮轨系统固有特性和钢轨纵向磨耗特征。结果表明：凹坑缺陷改变了轮轨滚动接触黏滑分布,导致轮轨界面发生滑移并诱发轮轨系统失稳,且滑移会进一步引起钢轨磨耗,以致最终可能形成波磨。综合轮轨接触黏滑特性和复模态分析的结果,可将钢轨波磨的形成机理归为轨面缺陷激励引发的轮轨系统的固有不稳定振动,且该不稳定振动表现为钢轨相对于轨道板的垂向弯曲振动。当车轮经过凹坑缺陷时,会产生瞬态纵向波动磨耗,且磨耗的特征波长为40～50 mm,这与实测线路上的波磨波长情况相符,从而进一步验证了钢轨波磨的形成机理。     

车轮型面对轮轨黏滑特性影响

利用非Hertz滚动接触理论和数值程序CONTACT分析了LM,LMA,S1002和XP55四种车轮型面与我国CHN60钢轨匹配时的轮轨黏滑特性.数值结果表明:四种车轮型面与CHN60钢轨匹配时的轮轨接触斑黏滑特性明显不同,车轮型面对轮轨接触斑面积、黏滑区分布、轮轨摩擦功等有较大影响;LM型面与CHN60匹配时的蠕滑区面积和轮轨摩擦功较大,且接触斑更容易达到饱和状态;LMA型面与CHN60匹配时的黏滑特性较佳,其接触斑面积、黏着区面积较大;S1002型面与CHN60匹配时的黏滑特性较XP55型面要好.     

U75V焊接接头三维轮轨滚动接触有限元分析

由于焊接区材质的非均匀性,钢轨焊接接头一直是钢轨伤损的频发区域,通过分离式霍普金森压杆实验获得了U75V钢轨在不同应变率下的应力—应变曲线,确定了Johnson-Cook冲击动态本构模型材料参数,建立了含焊接接头的轮轨滚动接触有限元模型;对钢轨焊缝区、热影响区和母材区的接触压力、等效应力和等效塑性应变进行了有限元分析.结果显示:在轮轨滚动接触过程中,焊接接头热影响区最大接触压力相对于相邻区域较小,与其他区域交界处产生明显的应力集中,其等效塑性应变最大处位于钢轨次表层,焊接接头的等效塑性应变大于母材,轴重的变化对焊接接头最大接触压力和等效塑性应变的影响较小;随着行车速度增大,热影响区域最大接触压力和焊接接头等效塑性应变均逐渐增大.     

地铁车轮凹陷磨耗对踏面接触应力的影响

针对地铁列车运营后出现的车轮踏面滚动接触疲劳现象,利用有限元软件ABAQUS建立考虑轮轨真实几何关系的三维弹塑性轮轨接触数值仿真模型,结合现场调查车轮磨耗结果和轮轨接触几何关系分析,计算分析车轮不同凹陷磨耗状态对踏面材料应力应变状态的影响。研究结果表明:车轮踏面主要凹陷磨耗区域为车轮踏面横向位置-30～50 mm处,轮轨接触几何关系呈强非线性特性,其轮轨接触点位置集中在车轮踏面横向位置20～32 mm或-32～-20 mm。车轮不同凹陷磨耗状态下的轮轨接触状态差异显著,在磨耗突变区(-30～-20 mm)轮轨接触斑呈狭长椭圆分布,导致相同载荷下轮轨接触应力较大。当轮对向外轨横移时,车轮凹陷磨耗接触区域材料易进入屈服状态,此时车轮踏面沿接触斑深度方向0～3.6 mm范围内Von-Mises等效应力最大,踏面表层材料等效塑性应变最大。车轮踏面出现凹陷磨耗后,车辆频繁地通过小半径曲线时易在磨耗突变区造成较高的等效应力和等效塑性应变,从而导致轮缘根部表面材料产生剥离损伤。     

摩擦系数对滚动接触疲劳裂纹萌生和磨耗影响

提出了疲劳裂纹萌生与磨耗共存发展离散化过程建模设想,根据临界平面法材料疲劳损伤理论和Archard磨耗理论,建立钢轨三维疲劳裂纹萌生与磨耗共存发展预测模型,分析轮轨接触位置的摩擦系数对曲线段钢轨表面疲劳裂纹萌生与磨耗发展的影响.结果表明,摩擦系数对接触斑面积、形状和位置无影响,但影响轮轨接触斑黏着区/滑动区的分布和切向应力状态;随着摩擦系数的增大,钢轨的平均磨耗发展率增加、磨耗量增大、裂纹萌生寿命减小,其中,摩擦系数从0.3增大至0.7时,外轨和内轨的平均磨耗发展率分别增大了约17%～55%、16%～42%,外轨和内轨的裂纹萌生寿命分别降低约24%～34%和18%～35%;随着摩擦系数的增加,外轨的裂纹萌生位置从轨面以下2.0～2.5mm处向亚表面0.9～1.0mm移动;内轨的裂纹萌生位置基本处于轨顶面下2.4～2.6 mm;轮轨接触位置的摩擦系数控制在0.3～0.4的范围,可以达到延长钢轨疲劳裂纹萌生寿命、减缓钢轨磨耗的目的.     

重载铁路钢轨磨耗状态下的轮轨法向接触特性

基于三维弹性体滚动接触理论,对法向接触问题最小余能方程的影响系数和法向间隙进行修正,使其更适用于非平面接触问题的求解.以某重载铁路通过总重达100 Mt的CHN75型面磨耗钢轨为对象,车轮选取LMA系列原始型面,利用修正后的接触模型,研究在30 t轴重作用下的轮轨法向接触特性.结果表明:轮对横移量对轮轨接触特性影响较大,横移量在+12～+14 mm轮轨接触状态变化显著;其中,横移量在+12.9～+13.2 mm时出现两点接触,横移量增大至+14 mm时出现车轮轮缘和钢轨轨距角的接触.     

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.