闸片摩擦块排列方式对高速列车制动盘磨损深度的影响

制动盘的摩擦磨损是高速列车盘式制动工作失效的重要原因,且摩擦块的排列方式是影响制动盘最大磨损深度的重要因素。为研究摩擦块排列方式对制动盘最大磨损深度的影响,考虑摩擦温度、接触应力和相对滑移速度在制动过程发生变化,基于Archard磨损模型进行修正,利用Ansys有限元仿真软件,建立制动盘-闸片三维瞬态模型,采用列车在通过42号道岔紧急制动时的工况,仿真计算了不同摩擦块排列方式下制动盘摩擦面的最大磨损深度值。分析了最大接触应力,提出了“应力磨损因子”参数,用来表征应力对最大磨损深度的影响。提取了径向节点磨损深度,分析了摩擦表面的磨损形貌,给出了摩擦块不同排列方式对制动盘磨损深度的影响规律。该研究为改善制动盘磨损提供理论依据和新的思路,为今后铁路制动系统闸片结构的设计提供了借鉴。     

城际动车组铝合金制动盘热应力场仿真分析

制动盘温度和热应力分布对制动盘寿命和制动性能有着极其重要的影响.本文建立制动盘热固耦合有限元模型考虑了热流密度和对流换热系数随时间的变化,运用ANSYS有限元分析软件,采用直接耦合的方法,对初速度200 km/h城际动车组铝合金制动轮盘在紧急制动时的温度场和热应力场进行仿真分析.仿真结果表明,制动盘最高温度发生在制动后43 s,最大值为244℃;制动盘最大应力是243 MPa,出现在第65 s,铝基复合材料能满足制动盘温度、强度性能要求,也能满足该城际动车组的运行要求.     

带有ABS系统的汽车制动效能的研究

基于制动过程的能量转换及摩擦生热,通过对盘式制动器实际工作条件的分析和理论计算,建立了紧急制动过程中制动盘与摩擦片瞬态温度场分析的有限元模型.采用直接热力耦合有限元方法来分析制动器摩擦热的产生及其温度的瞬态分布.讨论在汽车制动时ABS系统对汽车制动效能的影响.     

盘式制动器旋转结合面的热-结构耦合特性

为探索盘式制动器制动盘与制动片之间的摩擦生热规律及其热流分配规律,应用有限元软件对汽车紧急制动过程进行模拟,研究了制动器在制动过程中温度场、应力场的分布规律及其变化特征.研究结果表明:在制动过程中,系统的应力场和温度场分布都不均匀,二者沿径向和轴向都有较大的梯度,而沿周向的梯度相对较小;由于热应力和机械应力的作用,制动盘会发生热变形,从而使接触状态改变,并导致压力分布的变化,而接触压力的变化反过来又影响摩擦热流的输入;制动盘的变形既是温度场和应力场耦合作用的结果,也是振动摩擦耦合作用的结果.     

汽车制动系统温度场及内部流场仿真分析

为研究制动系统在制动过程中温度场对制动系统内部流场的影响,采用理论分析和三维模拟分析的方法,运用Ansys软件对制动盘、制动块等进行三维建模,分析在制动过程中其温度场的变化;建立制动系统液压管路的简化三维模型,运用Fluent软件分别对单相制动液、制动液与空气的流动情况进行仿真,并对结果进行分析.研究结果表明:温度在制动盘与制动块上均呈现渐变的趋势,其中制动盘上的温度要远远大于制动块上的温度;制动系统内部流场为制动液与空气相混合的两相流状态,其内部流场相对于单相流时呈现出不稳定的状态,制动压力分布不均匀.研究结论分析了产生这样结果的原因,为汽车制动系统的优化提供一个方向.     

紧急制动工况下汽车通风盘式制动器瞬态温度场分布的研究

以某乘用车前轮采用的通风盘式制动器为研究对象,建立其热-结构耦合的3维有限元分析模型.在此基础上采用直接耦合法对该通风盘式制动器在紧急制动工况下的瞬态温度场进行仿真分析,获得整个通风式制动盘和摩擦片在紧急制动过程中温度场的分布情况及变化特性.结果显示:在整个紧急制动过程中,制动盘温度场的分布不是轴对称的,其在径向、周向及轴向3个方向上均存在着一定的温度梯度; 制动盘的最高温度出现在1.91 s,最高温度为227.1 ℃.同时对该通风盘式制动器进行了与仿真分析相同制动工况下的台架试验,所获得的实验结果与仿真计算结果基本一致,从而验证了仿真分析的有效性,为通风盘式制动器的设计及优化提供了理论基础.     

仿生制动盘热-结构耦合场的ANSYS仿真分析

汽车制动盘在紧急制动下易发生热衰退导致的制动性能失效现象,从而引起事故的频繁发生.基于昆虫体表因具有非光滑表面结构而表现出的耐磨特性,构建了制动盘表面微结构仿生模型.根据热分析理论,对模型进行了不同初始速度下摩擦制动过程中瞬态温度场的仿真分析,研究了仿生制动盘表面微结构对散热性能的影响.结果表明:表面具有微凹坑结构的制动盘表现出较好的散热性能,利于制动性能的提高;这源于凹坑结构更易储存空气,能够实现制动盘与周围空气的快速换热,利于制动热量的迅速散失,从而有效降低因温度骤然升高而引起的热疲劳和热磨损.     

高铁制动盘不同分布热裂纹应力强度因子计算

为研究裂纹间的相互作用关系,应用扩展有限元法对高速列车制动盘进行热疲劳裂纹应力强度因子计算。采用有限元软件ABAQUS仿真计算得出制动盘在制动过程中的瞬态温度场及应力场,并将两组平行裂纹置于制动盘表面最高温度分布区域内,最后在线弹性断裂力学的框架下进行热疲劳裂纹应力强度因子计算。仿真结果表明:初速度为400 km/h的一次紧急制动模式下计算出制动盘峰值温度为638. 4℃,周向残余应力为375. 5 MPa。裂纹的径向与周向距离很小时,两裂纹尖端表现为屏蔽作用。随着其间距的增大屏蔽作用相应减弱。两条错位平行裂纹随着其径向距离的增加,尖端应力强度因子在小范围内会相互增强。     

不同表面凸起单元制动盘的热应力仿真分析

高速列车制动盘工作环境温度高,易产生热裂纹,影响行车安全.本文研究了光滑型、堤坝型、球型等具有不同形状表面凸起单元的制动盘的散热情况,基于热固耦合原理,对其进行热应力仿真分析.结果表明:表面带凸起的制动盘,其温度、应力变化率较大,常规光滑型制动盘温度、应力变化率较小;制动结束后,表面带凸起的制动盘温度、应力都低于光滑型制动盘,且温度、热应力降比均高于光滑型制动盘,3种制动盘温度降比分别为16.8%、27.3%、71.7%,应力降比分别为23.7%、46.1%、55.4%.制动盘表面的凸起单元,增加了热量消散的连通通道,可有效改善制动盘的散热效果,使制动后制动盘温度和应力值降低.     

通风盘式制动器热机耦合理论建模与分析

针对制动盘内外侧壁厚不等的通风盘式制动器,基于实测制动副摩擦系数一相对速度试验数据,建立了3维瞬态热-机耦合理论模型及有限元模型,分析了紧急制动工况下制动盘瞬态温度场和法向应力场在径向、周向和法向的分布特征,以及制动盘侧面热弹性变形和厚薄差变化规律.在台架试验中利用热电偶和非接触式位移计测量了制动盘表面温度和热弹性变形,仿真计算结果与试验结果具有良好的一致性,研究结果表明:制动盘瞬态温度、法向应力、热弹性变形之间存在复杂的耦合关系,这主要是由于制动盘通风槽和内、外侧壁厚不等的结构特点以及摩擦、热、机械的相互作用所致.     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

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.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

A computer generator for randomly layered structures

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

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.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the