进油口管径对液压冲击器冲击压力和流量的影响

为了给液压冲击器的系统研究及结构优化提供必要的实验依据,进一步研究了液压冲击器压力油入口尺寸变化对其动态压力和流量影响.以某冲击器做主要研究对象,利用测试液压冲击机械冲击性能的模拟载荷试验装置从试验角度对其进行实验,到了液压冲击机构工作中进油口管径尺寸对压力和流量影响的变化曲线和二者波动程度与油管直径尺寸之间的关系.结果表明:进油口管径直接影响液压冲击器冲击压力和流量的脉动值,在同频档下管径越小,冲击压力脉动愈大,则流量波动愈小.     

参数自适应型蓄能器磁流变液工作腔的分析

针对一种参数可变液压蓄能器样机(其充气压力、充气体积、工作介质阻尼系数及进油口结构参数能够根据液压系统工况变化实时调整),采用磁流变液作为其主要工作介质之一,通过磁流变液工作腔实时调整样机的阻尼系数,以满足不同液压系统动态特性的要求.重点研究磁流变液工作腔的结构及其外加电磁线圈磁路,在此基础上建立该部分数学模型,并将其与参数可变蓄能器样机整体数学模型结合进行理论分析,最后通过实验研究验证结构设计及理论分析的正确性.     

交变压力下溢流阀主阀口异常开启分析与优化

针对液压激振系统中存在交变压力的情况,为研究交变压力下先导式溢流阀的响应特性,对先导式溢流阀进行理论分析和AMEsim仿真分析,并进行试验对比研究.结果表明:交变压力下先导式溢流阀主阀口存在异常开启现象,增加系统能量损失;主阀口异常开启量随交变压力幅值增大而增大.通过减小主阀芯上腔容积、降低油液黏度和增大阻尼孔直径,可减小主阀口异常开启量.试验结果与仿真分析基本一致,验证了仿真分析的正确性与可靠性.     

负载口独立控制系统非线性滤波振动抑制方法

针对负载口独立控制系统在作业过程中时常因控制信号突变而造成执行器速度振荡及液压缸两腔压力波动,从而导致操作舒适性和机器可靠性降低甚至引发安全事故的问题,首先,分析了负载口独立控制系统压力流量复合控制策略以及传统阻尼补偿方法抑振的局限性,阐明了引发速度振荡与压力波动的原因;然后,基于该控制系统,提出了采用非线性滤波器修改突变控制信号的抑振方法,并给出了非线性滤波器的边界选取原则;最后,设计了负载口独立控制系统的进出口阀控制器,通过修改参考流量信号,降低了不同突变信号对执行器速度带来的影响。基于20 t挖掘机负载口独立控制系统开展数值仿真,结果表明：相较于传统阻尼补偿方法,采用所提方法能够有效降低阶跃、斜坡信号引起的执行器速度振荡与压力波动,且在动臂液压缸全伸、全缩典型工况下压力波动较小,并使速度振荡降低了32.5%～64.7%,从而有效改善了系统的动态特性。     

结构简单无位移死区的比例流量阀原理与模型

针对具有内部机械反馈的比例阀结构复杂、可靠性较低等问题,提出一种采用流量-位移反馈机制的三位四通比例流量阀原理与模型。给比例电磁铁施加电信号使先导阀芯产生运动,进而改变先导流量,使主阀芯两端压力失衡,主阀芯在压差作用下产生位移,而主阀位移又使主阀两端压力重新平衡,形成流量-位移反馈机制;以三位四通阀作为主阀使比例流量阀可以控制负载运动速度与方向;基于流量-位移反馈机制建立了三位四通比例流量阀的状态空间模型,推导出主阀芯位移与先导阀芯位移的近似函数关系。通过分析比例流量阀模型控制腔压力调节的范围,发现控制腔压力的下限值由零位时可变液阻等效面积与固定液阻直径决定,当阀芯离开零位时控制腔压力升高,其上限值为油源压力值。采用AMEsim仿真软件对所提出的三位四通比例流量阀模型进行仿真实验分析,分析结果表明：该比例流量阀结构简单、可靠性高,主阀芯位移与先导阀芯位移在零位附近为线性关系,且主阀阀芯位移在最大行程内没有死区;当控制腔压力为油源压力的0.3倍时,主阀阀芯位移在阶跃信号下响应时间为0.01 s,在同等条件下与传统比例阀相比提高了50%。     

新型系泊机构气动控制分支建模及摩擦力补偿试验研究

以新型系泊机构气动控制系统为研究背景,以其单个气动分支为例,建立了比例压力阀阀控缸动态数学模型,并对模型的正确性进行了实验验证;针对一腔形成位置闭环、另外一腔恒压力的独立负载口控制方式,通过将高频低幅的颤振信号叠加于恒压腔比例压力阀控制信号来对摩擦力进行补偿。仿真和实验结果表明,颤振补偿将系统定位精度从补偿前的1. 1 mm提高到补偿后的0. 5 mm。     

单级压力调节阀的阻尼孔射流响应特性分析

为揭示带阻尼孔的压力调节阀的稳定性机理,运用流固耦合方法计算了阶跃和周期性流量脉动信号激励下阀芯的响应过程,得出了不同阀腔结构条件下阀芯的轴向振动特征和阀口前端阀芯表面压力分布及其变化规律。研究发现,阀内阻尼孔射流流束冲击阀芯表面,使得阀口前端阀芯表面呈现射流冲击区和静压区两部分,阀芯的轴向振动幅值主要取决于射流冲击区和静压区二者液压力的相位差,当静压区和射流冲击区的液压力相位差趋于180°时,阀芯及其轴向振动幅值将大幅减小。研究结果为压力调节阀的设计提供了新思路。     

具有非对称阻尼网络平衡阀的动态特性分析

以具有非对称阻尼网络的LHDV型平衡阀为研究对象,建立了平衡阀控非对称液压缸的非线性数学模型,求解绘制了平衡阀阀口位移过流面积曲线,研究了重载低速超越负载液压缸下放工况时平衡阀的动态特性,获得了系统瞬态响应过程中各被控腔压力、通过各阻尼元件的流量、平衡阀主阀阀芯及液压缸位移的变化曲线.结果表明:该非对称阻尼网络具有压力削波、幅值衰减和方向阻尼作用,使平衡阀瞬态响应过程中开启比下降,阀芯运动具有快速开启慢速关闭特性,可有效抑制系统振荡;可调阻尼孔对平衡回路动态特性具有良好的微调特性,非对称阻尼网络具有良好的工况适应性.     

比例阀应用

分析了加热炉步进装置液压比例控制系统比例阀的斜坡时间，计算了比例阀口压差以及用比例阀控制时液压缸有效作用面积和液压泵压力，对于计算值给出了相应的测试结果。     

基于Morris法分析的液压参数对互联悬架的影响

针对液压参数对液压互联悬架输出响应影响强度大小的问题,在Matlab中建立了液压互联悬架半车侧倾耦合频域模型,根据系统的传递函数和路面输入得到了垂直和侧倾输出加速度谱密度并将其与传统悬架进行对比,分析对比结果.采用Morris灵敏度分析方法计算得到各液压参数的灵敏度值并进行灵敏度排序.结果表明,由于在侧倾振动中液压油频繁地流进和流出蓄能器,蓄能器参数及与蓄能器连接的阻尼阀压力损失系数对侧倾振动模态有较大影响;与作动器上下腔连接的阻尼阀压力损失系数对垂直振动模态有较大影响,所得结果为进一步的悬架优化中设计变量的选取提供了理论依据.     

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