偏转板伺服阀前置级结构参数优化研究

通过改变偏转板伺服阀劈尖高度和V形槽下端喷口的导流长度等结构参数,建立新的偏转板前置级模型,利用ICEM和FLUENT软件对前置级流场进行静态特性分析;对前置级流量曲线进行二次拟合,建立伺服阀系统数学模型,利用SIMULINK仿真模型进行动态仿真,分析偏转板伺服阀系统的动态特性,从而优化偏转板伺服阀前置级结构参数。结果表明,适当降低偏转板伺服阀劈尖高度,保持劈尖宽度不变,可增大偏转板伺服阀前置级的流量增益和提升伺服阀的响应频率;增加V形槽喷口的导流长度,会减小偏转板伺服阀前置级流量增益和降低伺服阀的响应频率。     

偏转射流式伺服阀研究综述

介绍了近15年针对传统结构偏转射流式伺服阀的动态性能及其前置级流场特性的研究进展.论述了近几年内偏转射流式伺服阀结构的改进与优化、射流盘加工工艺及检测手段的改善.探讨了不同新型材料在改善此类伺服阀静动态性能中的应用.偏转射流式伺服阀在温度因素影响下的热特性研究及在前置级冲蚀磨损效应影响下的性能改善和寿命预测将是未来的重要研究方向.     

偏转板伺服阀前置级压力特性数值模拟分析

利用SolidWorks软件建立偏转板伺服阀前置级流场模型,运用ICEM和Fluent软件计算分析前置级接收孔处圆角大小、偏转板厚度以及偏转板位置对偏转板伺服阀前置级压力特性的影响。结果表明,适当减小前置级接收孔处圆角半径,有利于提高偏转板伺服阀的灵敏度,当接收孔处圆角半径为0.05 mm时,前置级恢复压力曲线和压力差曲线的线性度最好,偏转板伺服阀的灵敏度最高;适当增加偏转板厚度,有利于提高偏转板伺服阀前置级的恢复压力,但会降低偏转板伺服阀的灵敏度;偏转板向左上偏转一定角度时,偏转板伺服阀前置级左右接收孔存在压力差,会导致作用于滑阀的合力不为零,不利于阀芯运动的控制。     

射流偏转板劈尖形变对其零位特性的影响

采用RNGk-ε湍流模型和气穴模型对射流偏转板伺服阀的前置级三维流场进行了仿真,分析了劈尖微小形变对伺服阀前置级射流气穴强弱、零位压力增益、零位流量增益和泄漏流量的影响.结果表明:劈尖为平顶时气相体积分数最高;随着偏转板位移的增大,前置级气相体积分数呈增大趋势;劈尖为平顶时前置级压差较大、零位压力增益比其他结构分别大21.5%和26.0%;劈尖为尖顶时前置级流量较大,零位流量增益比其他两种结构大19.1%和18.6%;劈尖为尖顶时前置级泄漏流量为7.51mL/s,泄漏流量最小;随着偏转板位移的增大,泄漏流量基本不变.     

一种气动位置伺服系统的辨识建模方法

针对具有强非线性特性的气动位置伺服系统,难以建立能较准确反映系统特性的线性化数学模型这一问题,该文提出采用基于"灰匣子"的系统辨识法建立比例流量阀控摆动气缸位置控制系统的数学模型,该方法依据摆动缸两腔压力差动态过程与摩擦力无关的特点,将压力差动态过程近似线性化方程与运动方程相结合,构成三阶状态空间模型,采用闭环定位辨识的方法确定模型中的参数.仿真和实验结果表明:采用该方法建立的数学模型能够反映实际系统的动态特征,所提出的建模方法是可行的.     

射流管伺服阀反馈杆刚度特性研究(英文)

建立了射流管伺服阀反馈杆的刚度数学模型.射流管伺服阀反馈杆为特殊的弹簧元件,可以通过恰当地设计反馈弹簧来实现射流管伺服阀的良好动态特性.同时还构建了反馈杆刚度的优化模型,通过有限元分析进行反馈杆刚度的分析和预测.     

高速开关阀控上下料机械手的气缸伺服系统研究

针对现有的比例阀控制气缸运动位置伺服系统的成本高、抗污染能力差等问题,文章分析了高速开关阀的开关特性,气缸的流量特性以及热力学特性,建立了系统的数学模型;并在传统的控制回路中增加BP(back propagation)神经网络控制器,该控制器可以根据系统实际输出和期望输出的偏差,在线调整PID(proportion integration differentiation)控制器的控制参数;以上下料机械手中的DGPL型气缸为控制对象,进行气动位置伺服控制的仿真研究。仿真实验表明,在系统参数相同的条件下,基于BP神经网络的PID控制效果优于传统方法的控制效果,能够实现气缸位置伺服系统的高精度控制。     

伺服阀力矩马达衔铁组件的振动特性分析

为揭示伺服阀自激噪声的产生机理,提出对伺服阀力矩马达的振动特性进行研究.给出一种射流管伺服阀力矩马达的结构及工作原理,基于结构力学基本原理,建立该射流管伺服阀力矩马达衔铁和射流管组件的的振动特性有限元分析数学模型,采用有限元分析方法,分析伺服阀力矩马达衔铁和射流管组件的前6阶振型,计算各种振型下伺服阀力矩马达衔铁和射流管组件的固有频率.研究结果表明,衔铁和反馈杆为伺服阀力矩马达产生振动的关键部位,为防止共振的发生,应尽量消除射流流场中与衔铁组件固有频率相接近的压力脉动激励信号.     

固体颗粒对射流偏转板伺服阀前置级冲蚀磨损的影响

针对射流偏转板伺服阀油液中的颗粒在高速射流时对其前置级产生冲蚀磨损的问题,将计算流体动力学和冲蚀磨损理论相结合,对射流偏转板伺服阀前置级进行了数值计算.模拟前置级油液的流动及固体颗粒的运动轨迹,计算了不同直径颗粒的最大运动速度及对前置级冲蚀磨损率的影响,分析了不同偏转板位移、V形导流窗口夹角以及不同偏转板厚度与前置级冲蚀磨损率的关系.结果表明:固体颗粒主要对劈尖冲击发生冲蚀磨损,油液中固体颗粒的直径越大其运动速度越小,但较大直径颗粒对前置级的冲蚀磨损较大;偏转板位移、V形导流窗口夹角以及偏转板厚度增大时前置级冲蚀磨损率减小.     

伺服阀非线性特性建模的液压弯辊系统动态特性

伺服阀非线性特性是影响液压系统动态性能的重要因素.通过对伺服阀非线性特性的分析,建立了相应的数学模型,并将其应用于工程实践中,建立了基于伺服阀非线性特性的液压弯辊系统的动态分析模型,利用软件MATLAB的工具箱SIMULINK实现了系统的动态仿真,得到较为满意的结果.     

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.     

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…     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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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。     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

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