多孔质气体静压径向轴承的Fluent仿真与实验研究

多孔质气体静压轴承相比传统的小孔节流轴承具有更高的承载能力,更好的稳定性及便于加工等优点。应用基于有限体积法的软件Fluent分析偏心率、多孔质材料渗透率、轴承长径比和平均气膜厚度等关键因素对多孔质径向轴承静态性能的影响,分析结果显示,在给定轴承平均气膜厚度的情况下,存在最佳的渗透率区间使得承载能力最大,增加轴承长径比和减小平均气膜厚度均可以提高多孔质径向轴承的承载能力及刚度,但需要根据加工装配工艺要求及实际工况选择合适的参数。设计制造中心供气新形式的多孔质径向轴承,通过仿真得到气膜间隙的压力分布及承载能力,并通过实验验证仿真结果的正确性。仿真和实验结果表明,该结构形式的多孔质径向轴承承载性能优良。     

基于分形理论多孔质石墨渗透率的研究

针对用于多孔质气体静压轴承的多孔质石墨结构的复杂性,从其结构形成机理出发,利用分形几何理论, 对多孔质气体静压轴承性能的影响起至关重要作用的渗透率进行研究,并建立多孔质石墨渗透率与其分形维数之间的定量关系,使多孔质石墨的宏观参数与微观结构建立联系。利用Matlab软件编写的程序,对多孔质石墨的组织结构进行分析,确定孔隙的分形维数,通过模型求得多孔质石墨的渗透率,并通过试验验证了模型的正确性。     

基于分形理论的多孔质气体止推轴承倾斜研究

多孔质节流器表面孔隙分布的不均匀性会导致多孔质气体轴承的倾斜。为寻找一种合适的方法来评价渗透率分布对多孔质轴承倾斜的影响,通过图像采集得到多孔质节流器表面孔隙的局部分形维数,然后利用局部分形维数的分布情况来评价渗透率的不均匀性,并提出分形维数分布向量来评估多孔质轴承的倾斜。通过实验测量多孔质轴承工作状态下的倾斜角度和方向。实验结果表明,该方法可以在不破坏多孔质节流器的情况下很好地预测多孔质轴承的倾斜:局部分形维数分布越集中则表明多孔质节流器的渗透率越均匀;根据分形维数分布向量的模可判断出轴承倾斜的角度大小,轴承倾斜的方向和分形维数分布向量的方向和达到了很好的吻合。     

多孔质静压气体轴承材料的研究

文内介绍了用粉末冶金材料制造多孔质静压气体轴承的优点、多孔质材料的制造工艺、加工静压气体轴承的方法与所使用的刀具、影响多孔质材料透气系数K值的主要因素及所采取的相应措施。附图2幅。     

基于分形理论多孔质石墨渗透率的研究

针对用于多孔质气体静压轴承多孔质石墨结构的复杂性。从其结构形成机理出发。利用分形几何理论，对多孔质气体静压轴承性能影响起至关重要作用的渗透率进行研究。并建立多孔质石墨渗透率与其分形维数之间的定量关系。使多孔质石墨的宏观参数与微观结构建立0联系。     

局部多孔质气浮止推轴承的设计研究

建立了局部多孔质气浮轴承的理论模型，该模型考虑了轴承气膜交界面处的切向速度滑移。利用有限元方法对所建立的模型进行了理论仿真，轴承静态特性的仿真与试验结果取得了较好的一致性，说明经过修改后的雷诺方程可以用来作为局部多孔质气浮轴承研究的理论模型。利用该模型成功计算出不同渗透系数、不同厚度及不同直径的局部多孔质气浮轴承的流量、承载及刚度特性，并给出了相应的变化曲线。根据仿真结论，提出了局部多孔质气浮止推轴承的设计准则。另外，从理论上将该类轴承与全多孔质类型气浮轴的承特性进行了对比，表明局部多孔质气浮轴承有着优良的特性，有很好的应用前景。     

多孔介质空气轴承静态特性仿真分析

多孔介质空气轴承作为气浮导轨的关键零部件,其静态特性对导轨性能至关重要。采用有限体积法进行了多孔介质空气轴承静态特性仿真,设计了多孔介质平板试验。采用可压缩Forchheimer方程获得多孔介质的渗透率系数;采用X-ray断层扫描方法分离了多孔介质内部孔隙结构,并将孔隙结构细分获得孔隙度。分析了多孔介质CT三维扫描图像的最小重复单元。基于CFD方法对多孔介质空气轴承静态特性进行了数值模拟,对网格数量无关性进行了验证。结果表明:通过合理设计多孔介质的形状和大小以及气膜的厚度,空气轴承能够获得较好承载力和静刚度。     

多孔质气体静压径向轴承倾斜状态特性研究

为研究倾斜状态对多孔质气体静压轴承性能的影响,基于一维流动模型应用有限元方法对多孔质气体静压轴承进行数值分析,研究渗透率、初始偏心距、倾斜角度等重要因素对多孔质径向轴承承载能力和弯矩的影响。结果显示:轴承初始偏心距对轴承承载能力影响很大;在相同初始偏心距时,倾斜状态下的径向轴承承载能力随着轴承倾角的增大而增大;在相同倾斜角度时,径向轴承承载能力分别随着轴承初始偏心距和轴承渗透率的增大而增大,并且初始偏心距越大,渗透率对承载能力的影响越大。     

多孔质电极电火花加工工艺

多孔质电极电火花加工采用多孔材料作为工具电极。多孔质电极由紫铜颗粒经高温烧结获得,在加工过程中可利用颗粒间孔隙形成的流道实现分布式的全向内冲液。通过制备符合电火花加工要求的多孔质电极并搭建实验系统,对多孔质电极的电火花加工性能进行了实验研究。经与实体电极进行对比发现,在工件上表面加工较浅的型腔时,由于多孔质电极表面不平整,易发生大量的侧向放电,其在材料去除率方面与实体电极相比没有优势;而在深孔中加工时,由于排屑条件恶化,采用多孔质电极后可利用分布式的内冲液极大改善极间状态,并可采用不抬刀方式加工,相同条件下材料去除率达到实体电极的4倍。     

空气静压多孔质止推轴承多孔质圆板的变形

在获取空气静压多孔持轴承的静态性能的过程中，有很多问题需要慎重考虑，其中包括惯性效应，速度滑移，多孔质渗透率的变化，多孔质表面粗糙度以及多孔质平板的变形，给出了止推轴承中多孔质平板的变形原理以及相应的粘结剂的弹性变形，同时给出了测量多孔质平板变形的方法和相应迭代方法的原理。     

三绕组变压器的双绕组等效建模及在Matpower中的应用

针对实际电网存在着大量的三绕组变压器,但国际上一些著名商业软件,如BPA仿真软件、Matpower这一权威潮流计算开源软件,均只提供双绕组变压器模型,限制了其在具有三绕组变压器的电力系统中的应用的问题,潮流计算是自主开发的电力系统各种应用软件的核心模块,因此依托国际权威开源程序进行二次开发,是一种较好的选择。对Matpower要求的数据格式进行了归纳,对变压器的一般的等值电路及带理想变压器的等值电路和带标幺值的等值电路进行了分析研究,提出了三绕组变压器转换为双绕组等效模型的建模方法,使得原先只适应双绕组变压器的潮流计算软件可以适用于三绕组变压器电网的潮流计算;最后以Matpower软件为例进行了案例计算,并用PSASP仿真软件进行对比验证。研究结果证明,所提出的建模方法是有效的。     

On the Relation of Load to Average Gap in the Contact Between Surfaces with Longitudinal Roughness

A computer simulation model for the contact between longitudinally-oriented rough surfaces has been formulated. This model closely duplicates the actual surf ace contact deformation behavior by taking into account the elastic interactions between the asperities. There were no assumptions made about the shapes, or any deformation behavior of the asperities, except for their obeying the laws of elasticity. The plastic deformations on the high asperity peaks were taken into account by setting a ceiling on their contact pressures at the material hardness value. The simulations used real surface profiles which were digitized from unworn circumferentially ground steel surfaces. Each pair of these profiles was mathematically combined to form an equivalent rough profile pressing against an infinitely rigid flat and having the appropriately adjusted elastic modulus. A total of 28 different pairs of profiles were used in the simulations. Each contacting pair was subjected to 30 different load levels and the local contact pressures and deformations were calculated. The contact simulations yielded some important mathematical relationships between parameters, such as the real area of contact, average gap, and average asperity load through statistical curve fitting. Two analytical functions were generated to relate the average load to average gap and the real area of contact to load.     

电站锅炉模糊风险评价方法研究与应用

针对电站锅炉风险等级评价问题,将模糊综合评价技术应用到电站锅炉风险等级评价中。开展了电站锅炉失效影响因素及模糊评价因素的重要程度分析,建立了一套科学合理适于在线评价的电站锅炉风险评价体系,提出了模糊综合评价技术与改进的模糊层次分析法相结合的模糊风险评价方法,利用改进的模糊层次分析法计算了指标体系中各层指标权重。对某一台电站锅炉的实际运行工况影响子因素进行了模糊风险评价,采用模糊合成算子进行模糊综合运算得到电了站锅炉运行工况影响子因素的评价向量。研究结果表明:电站锅炉的运行工况影响子因素的风险评价等级为第6级,失效可能性等级为小,该电站锅炉运行工况良好。     

交通荷载作用下桥梁结构参数识别方法

应用动力节点加载法,将作用在桥梁上的交通荷载转化为等效节点荷载,再用两步构造法识别结构物理参数.第1步,用Newmark-β方法变换结构运动方程,并用结构的加速度响应求得变换空间内的位移、速度和加速度响应;第2步,基于最小二乘原理,构造出变换空间内求解结构参数的递推式,进行结构物理参数识别.数值模拟结果表明,在交通荷载作用下,该方法能够快速、准确地进行桥梁结构参数识别.     

RLS and LMS blind adaptive multi-user detection method and comparison in acoustic communication

RLS and LMS blind adaptive multi-user detection algorithm and multi-user detector was proposed to solve the problem of multi-user signal detection problem encountered in underwater acoustic communication networks.In simulation analysis,RLS and the LMS blind adaptive multi-user detector were designed and tested for synchronous and asynchronous multi-user communication process.The results of SIR comparison and MMSE comparison show that,both of the two methods can realize blind adaptive detection when any user change in multi-user communication,during this process,the training communication sequences are not needed.The RLS algorithm has about 5 dB higher in SIR compared with LMS algorithm,and the convergence velocity of RLS algorithm is also higher than LMS algorithm when the communication users change.RLS algorithm has better ability in multi-user detection than that of LMS algorithm,and it has great attraction and guiding significance for solving the problem of multiple access interference(MAI) in multi-user communication.     

Robust Impedance Control of Robots Using an Adaptive Interaction Force Observer

For robot interaction control,the interaction force between the robot and the manipulated object or environment should be monitored.Impedance control is a type ...     

Research on key techniques of expendable conductivity temperature depth measuring system

This paper analysis the developing of expendable conductivity temperature depth measuring system(XCTD)and introduce its principle of measuring about temperature,salinity and depth of ocean.Some key techniques are put forward.According to the real needs of XCTD,conductivity sensor with high sensitivity is designed by principle of electromagnetic induce,the ocean conductivity from induced electromotive force has been calculated.Adding temperature correction circuit would help to reduce error of conductivity measurement because of sharply changing temperature.Advanced temperature measuring circuit of high precision and the constant current source is used to weaken effect of self-heating of resistance and fluctuation of the source.On respect of remote data transmission,LVDS is a good choice for the purpose of guarantee the quality of data transmitted and the transmission distance is reaching to thousand meters in the seawater.Modular programming method is also brought into this research aimed at improve the stability,reliability and maintainability of the whole measuring system.In February,2015,the trials in South China Sea demonstrate that the developed XCTD realize effective measurement at a speed of 6 knots and detection depth at 800 m.The consistency coefficient of the acquired data is greater than 0.99 and the success rate of probe launching is above 90%.     

CHARACTERISTCS OF FLUID FILM IN OPTIMIZED SPIRAL GROOVE MECHANICAL SEAL

In order to investigate the sealing performance variation resulted from the thermal deformation of the end faces, the equations to calculate the fluid film pressure distribution, the bearing force and the leakage rate are derived, for the fluid film both in parallel gap and in wedgy gap. The geometrical parameters of the sealing members are optimized by means of heat transfer analysis and complex method. The analysis results indicate that the shallow spiral grooves can generate hydrodynamic pressure while the rotating ring rotates and the bearing force of the fluid film in spiral groove end faces is much larger than that in the flat end faces. The deformation increases the bearing force of the fluid film in flat end faces, but it decreases the hydrodynamic pressure of the fluid film in spiral groove end faces. The gap dimensions which determine the characteristics of the fluid film is obtained by coupling analysis of the frictional heat and the thermal deformation in consideration of the equilibrium condition of the bearing force and the closing force. For different gap dimensions, the relationship between the closing force and the leakage rate is also investigated, based on which the leakage rate can be controlled by adjusting the closing force.     

OPTIMIZATION METHOD ON IMPELLER MERIDIONAL CONTOUR AND 3D BLADE

An optimization method for 3D blade and meridional contour of centrifugal or mixed-flow impeller based on the 3D viscous computational fluid dynamics (CFD) analysis is proposed. The blade is indirectly parameterized using the angular momentum and calculated by inverse design method. The design variables are separated into two categories: the meridional contour design variables and the blade design variables. Firstly, only the blade is optimized using genetic algorithm with the meridional contour remained constant. The artificial neural network (ANN) techniques with the training sample data schemed according to design of experiment theory are adopted to construct the response relation between the blade design variables and the impeller performance. Then, based on the ANN approximated relation between the meridional contour design variables and impeller performance, the meridional contour is optimized. Fewer design variables and less calculation effort is required in this method that may be widely used in the optimization of three-dimension impellers. An optimized impeller in a mixed-flow pump, where the head and the efficiency are enhanced by 12.9% and 4.5% respectively, confirms the validity of this newly proposed method.     

5083H111轧制铝合金的低周疲劳行为

在室温下对5083H111轧制铝合金板三个典型方向——轧制方向(RD方向)、与轧制方向成45°角方向(MD方向)、垂直于轧制方向(TD方向)的试样进行了单轴对称应变控制的低调疲劳试验,研究了不同方向试样的循环变形行为和疲劳寿命差异。结果表明:铝合金板在三个方向上都表现出了明显的循环硬化特性,即在恒定的应变幅下,三个方向的响应应力幅均随着循环次数的增加而增大,并且外加应变幅越大,响应应力幅也越大;三个方向的低周疲劳ε-Nf曲线差别不明显;三参数幂函数寿命模型可以很好地预测5083H111铝合金的低周疲劳寿命。