涡旋压缩机的径向迷宫密封研究*

针对涡旋压缩机径向密封难以实现的难题,提出一种径向迷宫密封。用几何学和热力学方法证明基圆渐开线型涡旋压缩机径向光滑间隙密封中的泄漏气速达到声速,分析径向光滑间隙密封中泄漏气体的热力变化过程,根据临界截面上气体的气动热力特性,推导出考虑边界层摩擦损失的径向光滑间隙密封泄漏量的算法,根据能量方程和连续性方程,推导出判定径向迷宫密封中泄漏气速是否达到声速的判别式和径向迷宫密封泄漏量的算法。计算和实测两种密封在一系列相邻压缩腔压差对应下的泄漏量。理论计算和试验对比表明,给出的两种密封泄漏量的算法正确;径向光滑间隙密封和径向迷宫密封的泄漏量均随着相邻压缩腔压差的增大而增大;径向迷宫密封的直通效应随着相邻压缩腔压差的增大而更加明显;径向迷宫密封泄漏量实测值约为径向光滑间隙密封泄漏量实测值的79%,说明径向迷宫密封的密封性能优于径向光滑间隙密封的密封性能。     

活塞速度和压差对冲击气缸间隙密封性能的影响

利用FLUENT软件建立冲击气缸往复运动间隙密封的模型并结合实验测试系统对其密封性能进行研究。为控制和减小往复运动中间隙密封的泄漏量,分析活塞往复运动速度、间隙进出口压差对其的影响。结果表明,当密封间隙宽度不变时,冲击气缸往复运动间隙密封的泄漏量随入口压力增大线性增大,并且压差与泄漏量的变化率不受活塞速度变化的影响;当密封间隙宽度不变时,在相同的入口压力下,泄漏量随着活塞速度的增大线性增大;冲击气缸的操作压力变化范围小导致其对泄漏量的直接影响不大,但是不能忽略压力变化通过对速度的影响而引起泄漏量的增大。     

液压式配气系统O型密封圈动密封特性分析

利用ABAQUS软件建立活塞运动速度为4 m/s、介质压力为6 MPa、摩擦因数为0.3的液压式配气系统O型密封圈有限元分析模型,分析不同往复运动速度、预压缩率、介质压力对液压式配气系统O型密封圈动密封特性的影响。结果表明:O型密封圈密封面的接触压力随位移的变化而产生波动,接触压力随介质压力、预压缩率的增大呈线性增大,运动速度对接触压力影响不大,接触压力曲线波动幅度随运动速度、介质压力、预压缩率的增大而增大;O型密封圈与油缸之间接触面的动密封性能优于O型密封圈与活塞之间接触面;O型密封圈在推程时的动密封性能优于回程;预压缩率小于10%时,O型密封圈不能满足该液压式配气系统的动密封要求,要确保O型密封圈的密封性,需要选择合理的预压缩率。     

F级燃气轮机高压迷宫密封泄漏特性研究

以F级燃气轮机高压迷宫密封为研究对象,研究密封间隙、压比、密封齿厚对迷宫密封泄漏特性的影响规律,采用泄漏系数表征各种影响因素与密封泄漏量的函数关系。结果表明:相同压比条件下,密封间隙增大,泄漏系数增大,且增大的趋势变大;相同密封间隙下,随着压比提高,泄漏系数近似线性的增大;相同间隙和压比下,随着齿厚的减小,泄漏系数减小。     

分层采油泵迷宫密封槽结构对阻流效果的影响

分层采油泵内柱塞与泵筒间隙密封的间隙几何参数和密封槽结构对阻流效果皆有影响。为探究有限长度泵间隙下密封槽的槽宽和数量对泄漏量的影响,基于Naiver-Stokes方程建立产出液在间隙流动控制方程,基于计算流体动力学对间隙流场进行数值分析。以广泛使用的FCCYB38-28A型分层采油泵为例（其配合间隙有3种,分别为0.045、0.095及0.145 mm）,分析不同泵间隙下密封效果随密封槽的尺寸和数量变化的规律。结果表明：0.045 mm密封间隙下泄漏率随密封槽槽宽波动变化,先减小后增大;0.095、0.145 mm密封间隙下泄漏率随着密封槽槽宽增大而减小;0.145 mm密封间隙下,随密封槽数量增加泄漏率减小,但由于密封槽数量增多产生的透气效应使得泄漏率减小趋势逐渐趋于平缓;在给定密封长度和0.145 mm间隙下密封槽数量取21个、尺寸取1.5 mm×1.5 mm时间隙密封具有较好的阻流效果。     

涡旋压缩机径向迷宫密封迷宫槽的优化研究

针对涡旋压缩机的直通型径向密封效果欠佳的难题,提出了多种形式的迷宫槽结构。采用GAMBIT软件建立迷宫槽非结构化网格模型,利用FLUENT软件模拟计算了迷宫槽内的流体流动状态及泄漏损失,搭建迷宫槽的烟雾示踪剂试验台,结合试验分析了泄漏气体的泄漏流动状态及泄漏损失。结果表明:理论分析与模拟计算的泄漏损失情况相吻合;泄漏会随着间隙的增大和漩涡的增加而增大;槽型对泄漏量的影响会随着间隙的增大而逐渐减小;得到了双阶梯槽在间隙为0.002mm时的密封性能最好。为涡旋压缩机迷宫密封的优化设计拓宽了思路。     

考虑闭合效应的刷式密封泄漏特性研究

采用基于非线性Darcian多孔介质模型的Reynolds-Averaged Navier-Stokes(RANS)方程的数值方法研究实验测量的零间隙和具有间隙的刷式密封在不同压比和转速下的泄漏特性,提出针对刷式密封闭合效应的间隙修正公式。考虑闭合效应后具有间隙的刷式密封泄漏量的预测结果与实验数据吻合,验证所建立刷式密封闭合效应修正模型的有效性。研究结果表明:刷丝束顶部与转轴间的间隙导致刷丝束内部压力降低且具有较为明显的径向压差,径向压差的存在导致刷丝束产生闭合效应,进而减小了刷式密封的有效密封间隙;闭合效应使得刷式密封有效间隙随着压比升高而减小,数值计算刷式密封泄漏特性时考虑闭合效应可以显著提高预测精度;在相同压比和转速下,具有间隙的刷式密封的泄漏量明显大于零间隙刷式密封的泄漏量;刷式密封的泄漏量随着压比的增大而增大;在所研究的转速范围内转速对刷式密封的泄漏特性的影响有限。     

超高速涡轮泵机械密封热弹流润滑特性研究

以超高速涡轮泵用机械密封为研究对象,针对超高速工况下密封界面多场耦合变形行为和热弹流润滑特性不明等问题,建立密封动静环和润滑液膜的耦合数学模型,研究不同转速和密封压力下的密封界面润滑特性和端面变形行为,分析相应的密封性能变化规律。结果表明：超高速工况下密封端面产生沿泄漏方向收敛的液膜间隙,密封动环的高温热变形是主因;随密封压力的增大,液膜间隙的收敛角减小,最大膜厚和泄漏率增大,端面温升明显减小;随着转速的增大,液膜间隙的收敛角、端面温升和泄漏率增大,摩擦扭矩减小。建立的流固热力耦合模型可为超高速涡轮泵用机械密封端面的优化设计提供理论指导。     

一种液压缸串联式组合密封及流场分析

针对液压缸传统的活塞密封,如接触密封、间隙密封存在的不足,将接触密封与间隙密封沿活塞轴向有机集成,提出一种新型串联式组合密封结构。建立该结构的数值分析模型,通过数值仿真获得流场压力分布、密封圈变形与内泄漏特性,以及结构参数对密封性能的影响规律。结果表明：在进出口压力相同的情况下,相比于接触密封,组合密封的内部结构中压力损失更大,密封圈受到的压力和冲击更小,有利于减少密封件变形;组合密封结构中端部的间隙密封对油液实施了阻滞,使中间的密封圈承受的油液冲击和压力变弱,因而密封圈变形更小;组合密封的多级密封结构能更好地屏蔽泄漏,提升密封性能;组合密封内泄漏受间隙密封长度、密封间隙和油液压力的影响,增大间隙密封长度、减小密封间隙和油液压力,可减少泄漏量。内泄漏物理实验进一步表明,该组合密封能有效减少内泄漏量,提高密封性能,且在密封圈出现损伤故障时,仍能在很大程度上抑制或减少内泄漏,提高密封效果与可靠性。     

变截面无油涡旋压缩机轴向间隙泄漏模型的研究

为定量研究变截面无油涡旋压缩机轴向间隙泄漏,基于等熵层流流动理论,建立了变截面涡旋压缩机在任意主轴转角时轴向间隙泄漏量的计算模型。通过求解该模型,分析了泄漏量与泄漏线长度、涡旋齿齿厚、工作腔容积、腔体温度之间的数值关系,得出基圆半径、轴向间隙对泄漏量影响的变化规律。为了验证计算模型的准确性,利用FLUENT软件对涡旋压缩机的工作过程进行仿真模拟,得出泄漏气体的速度、密度,并计算出轴向间隙平均泄漏流量,将模拟结果和理论计算结果进行了对比。结果表明:2种方法所得到的泄漏量变化趋势基本一致,该研究为新型线涡旋压缩机涡旋盘的加工、装配和密封提供理论参考提供理论参考。     

Minimal Realization of Linear Graph Models for Multi-physics Systems

An engineering system may consist of several different types of components,belonging to such physical"domains"as mechanical,electrical,fluid,and thermal.It is t...     

INTEGRAL EQUATION METHOD＇S APPLICATION IN HOLE-EDGE STRESS OF COMPOSITE MATERIAL PLATE WITH DIFFERENT SHAPED HOLES

The strength of composite plate with different hole-shapes is always one of the most important but complicated issues in the application of the composite material. The holes will lead to mutations and discontinuity to the structure. So the hole-edge stress concentration is always a serious phenomenon. And the phenomenon makes the structure strength decrease very quickly to form dangerous weak points. Most partial damage begins from these weak points. According to the complex variable functions theory, the accurate boundary condition of composite plate with different hole-shapes is founded by conformal mapping method to settle the boundary condition problem of complex hole-shapes. Composite plate with commonly hole-shapes in engineering is studied by several complex variable stress fimction. The boundary integral equations are founded based on exact boundary conditions. Then the exact hole-edge stress analytic solution of composite plate with rectangle holes and wing manholes is resolved. Both of offset axis loadings and its influences on the stress concentration coefficient of the hole-edge are discussed. And comparisons of different loads along various offset axis on the hole-edge stress distribution of orthotropic plate with rectangle hole or wing manhole are made. It can be concluded that hole-edge with continuous variable curvatures might help to decrease the stress concentration coefficient; and smaller angle of outer load and fiber can decrease the stress peak value.     

Non-monotonic material contrast in scanning ion and scanning electron images

30 keV Ga⁺ focused ion beam induced secondary electron (iSE) imaging was used to determine the relative contrast between several materials. The iSE signal compared from C, Si, Al, Ti, Cr, Ni, Cu, Mo, Ag, and W metal layers does not decrease with an increase in target atomic number Z₂, and shows a non-monotonic relationship between contrast and Z₂. The non-monotonic relationship is attributed to periodic fluctuations of the stopping power and sputter yield inherent to the ion–solid interactions. In addition, material contrast from electron-induced secondary electron (eSE) and backscattered electron (BSE) images using scanning electron microscopy (SEM) also shows non-monotonic contrast as a function of Z₂, following the periodic behavior of the stopping power for electron–solid interactions. A comparison of the iSE and eSE results shows similar relative contrast between the metal layers, and not complementary contrast as conventionally understood. These similarities in the contrast behavior can be attributed to similarities in the periodic and non-monotonic function defined by incident particle–solid interaction theory.     

Application of Feature Extraction through Convolution Neural Networks and SVM Classifier for Robust Grading of Apples

This paper proposes a novel grading method of apples,in an automated grading device that uses convolutional neural networks to extract the size,color,texture,an...     

分布动态载荷识别的抗噪处理

针对正交多项式频域法在用多种响应对矩形薄板进行载荷识别中抗噪性较差的问题,综合运用平均法、矩阵预处理和奇异值截断法等方法对之进行改善,并引入空间映射的思想,将该方法的应用范围拓展为复杂的模型.利用仿真算例,证实了该方法具有较好的抗噪性.     

基于MELTAC-N平台的核电厂安全级DCS环网研究与测试

针对工程实践中环网通讯相关问题的处理缺乏理论基础及国产化安全级DCS平台的开发缺乏成熟经验借鉴问题,对基于MELTAC-N平台核电厂安全级DCS环网的软硬件实现进行了研究。提出了安全级DCS环网双环网冗余设计、光切换开关设计等硬件设计方法,以及以RPR协议为基础,采用全数据收发策略的软件设计方法。在CPR1000安全级DCS平台上对安全级DCS环网的可靠性及实时性进行了评价,并进行了容错能力、响应时间及响应时间稳定性测试验证实验。结果表明,基于MELTAC-N平台安全级DCS环网软硬件设计具有较好的容错能力及响应时间稳定性。     

Short-Term Relay Quality Prediction Algorithm Based on Long and Short-Term Memory

The fraction defective of semi-finished products is predicted to optimize the process of relay production lines, by which production quality and productivity ar...     

End-to-End Multiview Gesture Recognition for Autonomous Car Parking System

The use of hand gestures can be the most intuitive human-machine interaction medium.The early approaches for hand gesture recognition used device-based methods....     

The laboratory simulation of abrasive wear

Abrasive wear has long been recognised as one of the most potentially serious tribological problems facing the operators of many types of plant and machinery; several industrial surveys have indicated that wear by abrasion can be responsible for more than 50% of unscheduled machine and plant stoppages. Locating the operating point of a tribological contact in an appropriate operational ‚map’︁ can provide a useful guide to the likely nature and origins of the surface degradation experienced in use, though care must be exercised in choosing the most suitable parameters for the axes of the plot. Laboratory testing of materials and simulations of machine contacts are carried out for a number of purposes; at one level for the very practical aims of ranking candidate materials or surface hardening treatments in order of their wear resistance, or in an attempt to predict wear lives under field conditions. More fundamentally, tests may be aimed at elucidating the essential physical mechanisms of surface damage and loss, with the longer term aim of building an analytical and predictive model of the wear process itself. In many cases, component surface damage is brought about by the ingress of hard, particulate matter into machine bearing or sealing clearances. These may be running dry although, more usually, a lubricant or service fluid is present at the interface. A number of standardised wear test geometries and procedures have been established for both two- and three-body wear situations, and these are briefly described. Although abrasive wear is often modelled as following an ‚Archard’︁ equation (i.e. a linear increase in material loss with both load and time, and an inverse dependence on specimen hardness) both industrial experience and laboratory tests of particularly lubricated contacts show that this is not always the case: increasing the hardness differential in an abrasively contaminated lubricated pair may not always reduce the rate of damage to the harder surface.     

ANGULAR DISTORTION ALLOWABLE VALUE AND ASSESS METHOD OF WELD ON COKE TOWER

A graph as the new engineering method for estimate the safety of bulging deformation of coke tower is proposed. Through stresses analysis of circumferential weld of coke tower and comparing the stresses produced by pressure with heat stress of steady state, residual stress, bending stress produced by both itself weight and wind loads, it showed that the stresses produced by pressure on the angle distortion are the main factor of equivalent stress of the combined stress. After comparing four kinds of stress controlling conditions, the relation to stress with depth of angular distortion, grade of curvature of angular distortion and half of region of angular distortion has been inferred. Graph of deformation allowable value of coke tower for different condition by angular distortion and half of region of angular distortion has been plotted. The five steps for its engineering use have been explained. The lighter the grade of curvature is, the larger of bulge allowance, may be, and the bigger of depth of angular distortion may pose too. For the coke tower with a popular structure of Dg 5 400 mm×28 mm, the result by graph is nearly more than the result of two formulas formed by other research, the error is less than 7.0%. But, the graph can be easily applied to different size of angular distortion.