平衡阀对车辆液压驱动系统的影响研究

为了改善轮式越野车辆的安全性和稳定性,研究驱动系统中关键元件平衡阀对轮式越野车辆液压行走驱动系统性能的影响. 以某越野车辆的液压行走驱动系统为研究对象,建立平衡阀的理论分析模型,运用AMESim软件建立了越野车辆液压驱动系统模型,分析了平路行驶工况、下坡行驶工况下驱动系统中泵、液压马达和平衡阀的压力及转速变化情况,并通过试验验证了仿真模型的准确性. 分析结果表明：平衡阀在液压驱动系统中具有平衡负负载、防止供油不足及下坡时防止液压马达失速的作用. 针对下坡过程中的冲击现象. 通过对平衡阀阀芯控制端阻尼槽槽深和阻尼孔直径优化分析,发现改变阻尼槽的槽深可以有效减小压力冲击,槽深由0.55 mm降为0.35 mm时,背压可减小12.5%.     

基于AMESim的螺纹插装式缓冲溢流阀的缓冲特性

针对工程机械在启动、制动或换向时液压马达腔会出现很高液压冲击的现象,对一种螺纹插装式缓冲溢流阀进行特性研究.建立螺纹插装式缓冲溢流阀的AMESim仿真模型,仿真分析缓冲式溢流阀的阀芯阻尼孔直径、缓冲套节流孔直径、弹簧刚度等参数对液压马达压力特性的影响.研究结果表明,适当地减小阀芯阻尼孔直径,增大缓冲套节流孔直径,减小调压弹簧刚度,可以提高缓冲式溢流阀的缓冲性能.     

旋挖钻机回转制动能量回收系统设计与分析

为利用旋挖钻机在回转阶段的制动能量,提出一种基于二次调节技术和液压蓄能器的能量回收系统。通过分析上车回转的工况特点,运用功率键合图理论建立回转动能回收利用的数学模型。针对系统参数的不确定性及存在的外干扰,设计自适应模糊滑模控制器对回转速度进行跟踪控制,并利用李雅普诺夫函数证明控制系统的稳定性和收敛性。为对系统进行优化设计,仿真分析液压蓄能器容积、充气压力及回转制动时间这3个主要因素对系统工作性能的影响规律。研究结果表明:所提出的回转系统在制动时能有效地完成能量回收,其中,回转制动时间对系统工作压力和能量回收效率影响最大,而液压蓄能器容积和充气压力对能量回收效率影响较小,但对恒压网络压力波动影响较大。     

基于AMESim的精密整平作业车液压系统仿真

为了在新型地铁整平装置的设计研发基础上,进一步优化精密整平作业车液压系统的设计及其关键参数设定,绘制了精密整平作业车的液压系统原理图,利用AMESim软件分别对振捣系统、螺旋布料系统和调平系统进行了建模与仿真分析。仿真分析结果表明,随着振捣频率的增加,振捣马达流量波动越来越大,为保证振捣系统性能,振捣频率设计为30Hz;系统中加装蓄能器能够提升系统的稳定性和可靠性,降低液压冲击,延长液压元件使用寿命;阻尼孔直径影响调平油缸升降速度,阻尼孔直径增大,油缸升降速度也随之增大。为了保证整平工作质量,使升降速度处于标准范围内,最终确定阻尼孔A1的直径为0.9mm。     

无压力超调溢流阀的静压力性能仿真

基于无压力超调溢流阀的工作原理,建立了溢流阀的压力静态性能数学模型。从理论上分析了相关参数对溢流阀静压力性能的影响。利用AMESim对无压力超调溢流阀的压力静态性能进行分析。结果表明:适当增大主阀座直径和主阀芯锥角,减少主阀主阻尼孔和先导阀阻尼孔直径,有利于提高溢流阀的静态压力性能。     

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.     

激振系统与平衡阀频率匹配问题分析

针对液压激振系统工作频率对平衡阀启闭性能存在影响,为研究平衡阀与激振系统工作频率匹配的问题,对激振系统平衡回路、先导控制回路和主阀芯受力情况进行数学建模,利用AMESim仿真软件进行分析,并实验验证.仿真结果表明:在激振系统中平衡阀的工作存在非正常工作临界点,对设备安全运行存在较大隐患;非正常工作点出现的原因为单个激振周期小于平衡阀主阀芯启闭时间,其由先导控制腔建压与卸压的时间决定;先导控制回路阻尼孔3和系统控制压力对平衡阀频率匹配影响较大.实验结果与仿真结果相符合,验证了仿真分析的可靠性.     

旋挖钻机平台回转液压回路系统故障分析

在故障树分析法的基础上,本文以旋挖钻机的平台回转液压回路系统为研究对象,针对回路中常见的故障现象,建立其故障树并对其进行故障树分析。     

液压自由活塞发动机液压阀组特性研究

研究液压自由活塞发动机液压阀组动态特性.基于单活塞液压自由活塞发动机活塞运动规律,给出了其液压阀组形式,建立了阀组数学模型,对阀组的稳定性、频率响应、位移时间响应和流量特性进行了分析.结果表明:单活塞液压自由活塞发动机吸排油应分别采用反向和正向外流式锥阀;减小阀组的阀芯质量和黏性阻尼系数可减小阀芯运动与活塞运动之间的相位差,提高系统容积效率;排油阀开启过程瞬时开度大且阀芯运动受限位装置影响.     

液压缓冲滑车碰撞试验力学建模及数值分析

以液压缓冲滑车碰撞试验装置为研究对象,应用有关力学和流体力学理论,对碰撞过程中滑车和液压缸活塞的受力、运动以及液压缸的压力变化进行了分析。根据能量守恒原理,构建了滑车碰撞过程的力学模型和能量守恒模型,采用离散求解方法,对所建立的模型实现了数值求解。针对某一具体算例,深入研究了滑车质量、初始碰撞速度、阻尼孔直径等参数对碰撞过程的性能影响,得到了一系列规律性的曲线。结果表明:滑车的加速度随初始碰撞速度、阻尼孔长度增大而增大,随滑车质量、阻尼孔间距的增大而减小;碰撞过程中,滑车质量越大,滑车速度降低得越慢;阻尼孔长度越大、阻尼孔直径越小,速度变化得越快;滑车位移随滑车质量、初始碰撞速度、阻尼孔间距、阻尼孔直径的增大而增大,随阻尼孔长度的增大而减小。     

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.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

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