Oscillations of a viscous liquid in a cylindrical container

The natural damped frequencies of a viscous liquid in a circular cylindrical container are obtained for slipping and anchored contact line at the container wall r = a. In addition the response to translational forced excitation has been determined. The results may also be applied to viscous liquid in a micro-gravity environment, as long as the contact angle of the liquid surface to the cylindrical container wall is in the vicinity of π/2, indicating, that the free liquid surface equilibrium position remains a plane surface. It could be found that there exists in contrast to frictionless liquid a small filling range, in which the liquid performs only an aperiodic motion. The adherence condition at the side wall was replaced by the somewhat weaker condition of an anchored contact line.     

Asymptotically Stable Motions of a Gyro in a Spinning Vehicle

An analysis of the motion of a single-axis rate gyroscope mounted in a space vehicle which is spinning with uncertain constant angular velocity xz about the spin axis of the gyro is presented. The nonlinearity in the equation of motion of the gimbal is retained. Using the Lyapunov approach, regions are obtained in the k-xz plane where k is the torsional spring constant, for asymptotic stability and for global asymptotic stability, and an estimate of the region of stability in state space is presented. Analytical relations for the selection of the gyro parameters are derived.     

直升机起落架的集成计算

直升机起落架常规计算包括停机状态计算及减缩质量计算、静态性能计算及主、尾起落架的着陆性能计算.要完成这些计算需要整机及起落架的诸多数据.在研制过程中,为了获得最优的设计,需要对起落架的各参数进行不断调整,对计算结果进行反复分析和比较,计算量较大,数据处理较为繁复耗时.详细阐述如何采用Excel和Matlab对起落架的常规计算进行集成.为完成一种直升机起落架的常规计算,采用该集成方法,编制了2000余行的M代码.在惠普Z800计算机平台下运行,耗时400余秒即可完成所有相关计算.输入输出的数据存储在同一Excel文件,文件中各项参数和计算结果数据可直接用于查阅、校对、分析,也可再编辑.     

Performance of a Two-Sample Mann-Whitney Nonparametric Detector in a Radar Application

The detection of signals in an unknown, typically non-Gaussian noise environment, while attempting to maintain a constant false-alarm rate, is a common problem in radar and sonar. The raw receiver data is commonly processed initially by a bank of frequency filters. The further processing of the outputs from the filter bank by a two-sample Mann-Whitney detector is considered. When the noise statistics in all filters are identical, the Mann-Whitney detector is distribution free, i. e., the false-alarm probability may be prescribed in advance regardless of the precise form of the noise statistics. The primary purpose of this paper is to demonstrate the potential advantage of nonparametric detectors over conventional detectors. The signal detection performance of the Mann-Whitney detector is compared to that of an ordinary linear envelope detector plus integrator in the presence of Gaussian and several hypothetical forms of non-Gaussian noise. This comparison is made for both uniform and nonuniform distributions of noise power across the filter bank. Besides providing a much more constant false-alarm rate than the conventional detector, the Mann-Whitney detector's signal detection performance is found also to be much less sensitive to the form of the noise statistics. In one case, its detection sensitivity is found to be 11 dB better than that of the conventional detector. Even when the noise power density is made moderately nonuniform across the filter bank, the detection performance of the Mann-Whitney detector is found not to be significantly affected.     

长尾喷管中粒子运动轨迹的数值模拟

利用颗粒轨道模型计算了长尾喷管两相流流场,确定了在与壁面发生完全弹性和完全非弹性碰撞情况下不同尺寸粒子的运动轨迹,比较了不同尺寸粒子之间以及完全弹性碰撞和非弹性碰撞之间长尾喷管中粒子运动的差异,得出了长尾喷管中粒子运动的某些规律。      

粘性气体中粘性液体射流分裂与雾化机理研究

采用线性稳定性分析的方法对粘性气体中的粘性液体射流的分裂与雾化机理进行了分析,数值计算表明:液体射流分裂与雾化过程中存在一临界气体韦伯数We2c=1,We2＜We2c对应的是射流分裂过程,We2＞We2c对应的是射流雾化过程,射流分裂过程和雾化过程的机理有所不同.当We2＜1时,We2对射流分裂过程具有稳定性的作用;当We2＞1时,We2对射流雾化过程起着不稳定性的作用.液体Reynolds数Re1在整个射流过程中始终起着不稳定性的作用,气体Reynolds数Re2的作用却相反.气液密度比Q,即气动力在整个射流分裂与雾化过程中始终起着不稳定性的作用.     

Upper Bound of a Loop Gain in a Power Inversion Adaptive Array

A loop gain is an important parameter in a power inversion adaptive array. The upper bound value of the loop gain is obtained which prevents the array suppressing a desired signal seriously. This result is very useful for determining the loop gain.     

Internet中计算机的定位

从IP地址的角度 ,介绍IP地址的构成 ,IP地址与域名的对应关系和域名管理系统的作用。从而给予了每台计算机惟一定位。     

Mathematical Model of the Flow of a Liquid Film of Variable Thickness on a Flat Surface in a Viscous Gas Flow

The paper presents a mathematical model of the film flow over a half-plane directed at an angle to the horizon. In the cross section of the film, a quadratic law for the longitudinal velocity distribution is adopted, taking into account friction on the film surface. An approximate solution of the problem is obtained in the form of a series in powers of the small parameter. The solution is presented in the form of graphs of the film thickness and the average longitudinal velocity along the length of the plate.     

Time-domain modeling of a cutter exiting a workpiece in the slot milling process

In a milling operation, there must be processes of a cutter entering and exiting the work-piece boundary. The cutter exit is usually in the feed direction and the dynamic response is different from that in the normal cutting process. This paper presents a new time-domain modeling of mechanics and dynamics of the cutter exit process for the slot milling process. The cutter is assumed to exit the workpiece for the first time with one tooth right in the feed direction. The dynamic chip thickness is summed up along the feed direction and compared with the remaining workpiece length in the feed direction to judge whether the cutter is ready to exit the workpiece or not. The developed model is then used for analyzing the cutting force and machining vibration in the cutter exit process. The developed mathematical model is experimentally validated by comparing the simulated forces and vibrations against the measured data collected from real slotting milling tests. The study shows that stable cutting parameters cannot guarantee stable cutting in a cutter exit process and further study can be performed to control the vibration amplitude in this specific process.     

Extrinsic calibration of a laser displacement sensor in a non-contact coordinate measuring machine

In order to implement 3D scanning of those complicated parts such as blades in the aviation field,a non-contact optical measuring system is established in the paper,which integrates a laser displacement sensor,a probe head,the frame of a coordinate measuring machine (CMM),etc.As the output of the laser sensor directly obtained possesses the 1D length of the laser beam,it needs to determine the unit direction vector of the laser beam denoted as (l,m,n) by calibration so as to convert the 1D values into 3D coordinates of target points.Therefore,an extrinsic calibration method based on a standard sphere is proposed to accomplish this task in the paper.During the calibration procedure,the laser sensor moves along with the motion of the CMM and gathers the required data on the spherical surface.Then,both the output of the laser sensor and the grating readings of the CMM are substituted into the constraint equation of the spherical surface,in which an over-determined nonlinear equation group containing unknown parameters is established.For the purpose of solving the equation group,a method based on non-linear least squares optimization is put forward.Finally,the system after calibration is utilized to measure the diameter of a metallic sphere 10 times from different orientations to verify the calibration accuracy.In the experiment,the errors between the measured results and the true values are all smaller than 0.03 mm,which manifests the validity and practicality of the extrinsic calibration method presented in the paper.     

Inertial deposition of suspended particles in a flow around a porous cylinder

The results of studying a dispersed airflow around a single porous cylinder are presented. The flow field of carrying medium outside the cylinder is described within the framework of the Navier-Stokes equations for incompressible gas; inside the porous cylinder the Darcy-Brinkman extended equations for averaged velocity are used. The numerical solution of the medium equations is achieved in the FLUENT package. In the found field of carrying medium velocities the suspended particle trajectories are calculated. Also given are the dependences of the particle inertial deposition effectiveness on the Stokes number at various values of the Darcy number.     

高职教育办学特色的构建与实施

详细介绍了西安航专高职教育办学特色的理论基点和实践历程，分析了西安航专办学特色和做法，重点从明确服务面向、构建合作平台、建设实训基地、开展“订单”培养、实施能力本位和解决企业难题实现互动双赢这六个方面总结了西安航专校企合作开展人才培养的具体做法和取得的显著效果。     

宽马赫数范围高超声速进气道转动唇口变几何方案研究

结合简单一维流理论讨论了一种工作于Ma=4～7、采用可转动唇口的变几何二元高超声速进气道设计方案,并利用数值仿真手段对其Ma=4下的自起动性能及其他不同工作马赫数下的性能进行了研究.结果表明:所设计的变几何进气道必须辅以附面层排移措施才能在Ma=4下顺利实现自起动;该变几何方案Ma=4下的流量系数达0.7以上,这为飞行器加速提供了强有力保障;与定几何进气道相比,变几何进气道高低马赫数下的总体性能均得到显著提高;此外,转动唇口的铰接位置对自起动性能有重要影响.      

横向风影响下空冷塔内外流场的数值研究

用有限体积方法对有横向自然风环境下空冷塔的三维湍流流场及温度场进行了数值模拟，计算中采用了标准ｋ－ε湍流模式；对结果的分析揭示出刮风时空冷塔散热能力下降的主要原因，可为进一步提出防风措施提供理论依据。     

源项冷却模型的建模以及在平板和涡轮的应用

为了解决由于划分冷气腔和尺寸过小的多排气膜冷却孔导致网格量过大的问题,本文基于NUAA-Turbo平台,在气膜冷却孔出口处建立适用于变比热条件下的源项冷却模型来代替冷却气体从孔内流出,并且在孔内建立换热模型,用于模拟孔内的对流冷却。对气膜冷却平板算例气动研究发现:在吹风比为1.0时,计算值与试验值相吻合。而对吹风比为1.5的孔下游近壁处计算时,发现流向速度计算值与试验值存在11.1%的误差,但小于商用软件44.4%的误差,尽管发现优化后的源项冷却模型不能很好反映下游近壁处法向速度分布,但计算精度在商用软件源项冷却模型基础上有25%的提高。为了证明该方法的可行性,对气冷高压涡轮MT1导叶的等熵马赫数以及平均努塞尔数等相关实验数据与计算数据作了对比,研究发现:在吸力面和压力面计算值与试验吻合较好,而在无冷却气膜覆盖的叶片尾缘和叶片前缘等局部位置计算值与试验值存在误差。研究表明:优化后的源项冷却模型能够较为准确地模拟冷却射流的宏观特征,该方法对工程上气冷涡轮的设计有一定的应用潜力。     

Influence of the open end geometry on resonance oscillations of a gas in a tube

Resonance oscillations of a gas in an open-ended tube of different geometry are investigated. The calculation is made by means of a one-parametric model using the experimental data for a pointed end and flanged ends. The distributions of the absolute values for dimensionless amplitudes of gas velocity and pressure variations along the tube are presented. The theoretical calculations are compared with the experimental results.     

Mechanism of stall and surge in a centrifugal compressor with a variable vaned diffuser

To expand the stable operating range of compressors, understanding the mechanism of flow instability at low flow rates is necessary. In this paper, the mechanism of stall and surge in a centrifugal compressor with a variable vaned diffuser is experimentally investigated, where the diffuser blade setting angle can be adjusted. Many dynamic pressure transducers are mounted on the casing surface of the compressor. From the design condition to surge, dynamic pressure data is recorded throughout the gradual process. According to the signal developing status, the typical modes of compressor instability are defined in detail, such as stall, mild surge, and deep surge. A relatively high-frequency stall wave originates in the impeller and propagates to the diffuser, and finally stimulates a deep surge in the compressor. The compressor behavior during surge differs at different diffuser vane angles. When the diffuser vane angle is adjusted, both the unstable form and the core factor affecting the overall machine stability change. A specific indicator is proposed to measure the instability of each component in a compressor, which can be used to determine the best region for stability extension technologies, such as a holed casing treatment, in different compressor applications.     

用正弦规测量圆锥角实验的误差分析

本文定量分析了在用正弦规测量圆锥角的实验中定值系统误差、变值系统误差及偶然误差对测量结果的影响，给出了减少相应测量误差的方法，以达到相对准确的测量结果。