燃气轮机系统仿真集成概念及其分布对象实现

本文提出燃气轮机系统仿真集成的概念, 分析了关键实现技术, 然后从跨平台性入手, 给出 1个分布异构计算机平台上的面向对象实现方案。算例表明, 这一方案成功实现了系统仿真集成的主要功能, 从而为发动机系统的多学科开发、研制和实验提供了有效的仿真软、硬件平台, 并使发动机的远程协同设计成为可能。      

EXPERIMENTAL STUDY OF FLOW FIELDS IN THE VICINITY OF A FILM COOLING HOLE EXIT

Sofar,filmcoolingisextensivelyadoptedforprotectinghightemperaturepartsingasturbine.Manyresearchworksarefocusedonflow[1~3Jandheattransfer[4'5jinthedownstreamofthecircularhole,buttheflowcharacteristicsattheholeexit,especiallyforflaredholeexit,arenotreportedatpresent.Inordertodesignasuitab1eholeshapeforpracticalcoolingandprovideplentyexperimentaldataforverificationofcomputercodes,adetai1edexperimentalin-vestigationabout3-Dflowfieldsattheexitofasinglecircularandfan-shapedholehasbeencompleted.1Exp…     

Position-Location Solutions by Taylor-Series Estimation

Taylor-series estimation gives a least-sum-squared-error solution to a set of simultaneous linearized algebraic equations. This method is useful in solving multimeasurement mixed-mode position-location problems typical of many navigational applications. While convergence is not proved, examples show that most problems do converge to the correct solution from reasonable initial guesses. The method also provides the statistical spread of the solution errors.     

Ultra-lightweight space power from hybrid thin-film solar cells

The development of hybrid inorganic/organic thin-film solar cells on flexible, lightweight, space-qualified, durable substrates provides an attractive solution for space power generation with high mass specific power (W/kg). The high-volume, low-cost fabrication potential of organic cells will allow for square miles of solar cell production at one-tenth the cost of conventional inorganic materials. Plastic solar cells take a minimum of storage space and can be inflated or unrolled for deployment. We explore a cross-section of NASA in-house and sponsored research efforts that aim to provide new hybrid technologies that include both inorganic and polymer materials as active and substrate materials. For NASA applications, any solar cell or array technology must not only meet weight and AMO efficiency goals, but also must be durable enough to survive launch and space environments. Also, balance of system technologies must be developed to take advantage of ultra-lightweight solar arrays in power generation systems.     

TVD格式计算一维Euler方程间断解存在的几个理论问题

本文讨论了TVD格式按本文第二节A段意义推广到拟线性方程组的几个理论问题。指出:1.对于Riemann间断分解,Euler方程的解和Riemann不变量都没有TVD性质,因此不能将TVD格式自然推广;2.TVD格式是提高分辨率的一种途径,它不能保证得到物理解,能得到物理解的TVD格式一定是耗散守恒格式,因此将TVD格式推广时,必须保证格式是耗散的,否则仍会得到非物理解。并给出了一阶迎风格式,TVD2,UNO2得到的若干非物理解算例;3.非物理解现象只是发生在具有剧烈膨胀的单波区的计算上,而某些TVD格式若会得到非物理解,则一定发生在特征值变号的单波区的计算上。     

Pulsatory phenomenon in a thrust optimized contour nozzle

A numerical study of the flow in an axisymmetric overexpanded thrust optimized contour nozzle is presented. The separation flow structures at different pressure ratios are investigated. The start-up process exhibits two different shock structures. For a range of pressure ratios, hysteresis phenomenon occurs between these two separation patterns. For a larger pressure ratio, where the principal separation point is always inside the nozzle, another phenomenon appears. This phenomenon results in an oscillatory longitudinal quasi periodic movement of the separation structure. The computed nozzle wall pressures show a correct agreement with the experimental measurements and the pulsations frequency of the oscillatory phenomenon is also well predicted.     

Uncertainty analysis of turbulence model in capturing flows involving laminarization and retransition

Flows experiencing laminarization and retransition are universal and crucial in many engineering applications. The objective of this study is to conduct an uncertainty quantification and sensitivity analysis of turbulence model closure coefficients in capturing laminarization and retransition for a rapidly contracting channel flow. Specifically, two commonly used turbulence models are considered: the Spalart-Allmaras (SA) one-equation model and the Menter Shear Stress Transport (SST) two-equation model. Thereby, a series of steady Reynolds Averaged Navier-Stokes (RANS) predictions of aero-engine intake acceleration scenarios are carried out with the purposely designed turbulence model closure coefficients. As a result, both SA and SST models fail to capture the retransition phenomenon though they achieve pretty good performance in laminarization. Using the non-intrusive polynomial chaos method, solution uncertainties in velocity, pressure, and surface friction are quantified and analyzed, which reveals that the SST model possesses much great uncertainty in the non-laminar regime, especially for the logarithmic law prediction. Besides, a sensitivity analysis is performed to identify the critical contributors to the solution uncertainty, and then the correlations between the closure coefficients and the deviations of the outputs of interest are obtained via the linear regression method. The results indicate that the diffusion-related constants are the dominant uncertainty contributors for both SA and SST models. Furthermore, the remarkably strong correlation between the critical closure coefficients and the outputs might be a good guide to recalibrate and even optimize the commonly used turbulence models.     

我国经济改革与发展中失业现象的分析和思考

失业作为一种社会经济现象,有其产生和存在的客观必然性。社会主义不应否认失业,而应当认真地分析、研究社会主义条件下失业现象存在的原因和特点,寻找妥善解决的办法,为社会经济发展服务。     

Reduction of interference from DGPS transmissions in the MF bandusing a GMSK modulation scheme

The accuracy of the Global Positioning System (GPS) can be improved by differential techniques. For maritime applications a DGPS service with transmissions by maritime radiobeacons in the MF band is provided. It offers a position accuracy of approximately 5 m. For the data link a minimum shift keying (MSK) modulation scheme has been recommended. The adjacent channel interference at the maximum transmission rate might not be consistent with existing frequency plans     

Securing large applications against command injections

The ability to produce more secure software or to improve the security of existing software is a growing concern and a real challenge for the field of software engineering. Among the various existing types of software vulnerabilities, command injections are particularly common. It is a difficult problem to address, having seemingly endless variations. We present a unified, formal definition of command injections that, is not based on a particular technology and captures not only the existing variations but also the future instances of the problem. We then propose a Simple, yet effective, strategy to deal with the problem in existing large applications, focusing on the cost-effectiveness of the method. We also report on successful experiments applying our solution to large commercial applications.     

GTD Terrain Reflection Model Applied to ILS Glide Scope

The capability of calculating the reflection of electromagnetic signals from uneven terrain has many applications. One of these is the determination of instrument landing system (ILS) glide slope performance. For this application the wavelength is approximately 1 m, incidence angles are usually near grazing, and the fields are horizontally polarized, so that gross irregularities such as dropoffs and hills are more important than surface roughness. Past approaches used to calculate the ground reflections for this application have been three-dimensional physical optics models which were very cumbersome and time consuming and which neglected important diffraction and shadowing phenomenon; a two-dimensional physical optics model which was faster than the three-dimensional models but ignored many shadowing and transverse terrain variation effects; and a half-plane diffraction model which is applicable only to a specified type of terrain geometry. In this paper a terrain reflection model based on the geometrical theory of diffraction (GTD) is described which can accommodate any piecewise linear terrain profile, requires less computer time than the physical optics models, is capable of including transverse terrain effects, and determines the reflected fields with all important diffraction and blockage effects included.     

Remaining useful life prediction for engineering systems under dynamic operational conditions: A semi-Markov decision process-based approach

For critical engineering systems such as aircraft and aerospace vehicles, accurate Remaining Useful Life(RUL) prediction not only means cost saving, but more importantly, is of great significance in ensuring system reliability and preventing disaster. RUL is affected not only by a system's intrinsic deterioration, but also by the operational conditions under which the system is operating. This paper proposes an RUL prediction approach to estimate the mean RUL of a continuously degrading system under dynamic operational conditions and subjected to condition monitoring at short equi-distant intervals. The dynamic nature of the operational conditions is described by a discrete-time Markov chain, and their influences on the degradation signal are quantified by degradation rates and signal jumps in the degradation model. The uniqueness of our proposed approach is formulating the RUL prediction problem in a semi-Markov decision process framework, by which the system mean RUL can be obtained through the solution to a limited number of equations. To extend the use of our proposed approach in real applications, different failure standards according to different operational conditions are also considered. The application and effectiveness of this approach are illustrated by a turbofan engine dataset and a comparison with existing results for the same dataset.     

DQI-NP application to the OutriderTM Tactical UnmannedAerial Vehicle (TUAV)

A wide variety of applications can benefit from integrated Inertial Navigation System/Global Positioning System (INS/GPS) technology. However, in many situations, the end user has a preference for a specific GPS receiver. Additionally, in most cases, the user does not desire to expend the time and money necessary to perform a custom INS/GPS integration, but instead wants a low-cost off-the-shelf solution. To address these applications, Boeing has developed the Digital Quartz Inertial Measurement Unit (DQI IMU)-Navigation Processor (DQI-NP) product as an extension of its Miniature Integrated GPS/INS Tactical System (MIGITS^TM) family of integrated INS/GPS products. This paper describes the DQI-NP and its application to the Outrider^TM Tactical Unmanned Aerial Vehicle (TUAV). The DQI-NP, as currently integrated into the Outrider^TM TUAV, is coupled with a custom Trimble GPS receiver combined with major embedded firmware modifications by IntegriNautics. In conjunction with differential GPS and ground based pseudolites, the overall system is intended to provide autonomous landing capability to the Outrider TUAV. DQI-NP provides an available, low-cost, commercial-off-the-shelf/non-development item (COTS/NDI) solution to a variety of commercial and military applications, of which the Outrider ^TM TUAV is an excellent example     

航空发动机压气机内部流体诱发声共振研究进展

声共振是一种涡声相互作用诱发的特殊声学共振现象，可产生超过160 dB的纯音噪声，不仅严重影响环境舒适性，还可引起结构件的疲劳破坏，在火箭燃烧室、军机弹仓、汽车天窗以及热交换器管束等多个工程领域内引起了设计者们的足够重视。与此同时，越来越多的研究表明航空发动机压气机内部同样存在声共振问题，其引发的叶片断裂故障也屡见不鲜，已逐渐成为国际范围内的一项研究热点问题，但对其物理机制的认识仍待完善。本文系统性阐述了压气机内部声共振的机理、试验测试、预测方法和控制措施的研究现状及其发展趋势，旨在扩展对流体诱发叶片振动方面的基础理论认知，为提升压气机设计和排故能力提供技术储备。     

后掠机翼跨音速绕流的二级近似方法

本文采用TSDH方程计算三维后掠机翼的跨音速绕流,考虑了适用于机翼钝前缘的前缘边界条件和前缘速势方程。采用Jameson格式在不等步长格网中的推广形式,把TSDH方程离散化为差分方程组。然后,在整个计算空间内布置稀网,在机翼附近再布置密网,进行稀密网的交替迭代,以加速收敛和提高计算精度。对ONERA M6机翼的超临界无激波和有激波情况的计算表明,TSDH解与FVP解和风洞试验符合良好。     

Lock-in phenomenon of tip clearance flow and its influence on aerodynamic damping under specified vibration on an axial transonic compressor rotor

In this study, the lock-in phenomenon of Tip Clearance Flow(TCF) instabilities and their relationship to blade vibration are investigated numerically on an axial transonic rotor with a large tip clearance. The capabilities of simulating instability flow and lock-in phenomenon are verified on a transonic rotor and a NACA0012 airfoil by comparing with the test data, respectively.The lock-in phenomenon is first numerically confirmed that may occur to TCF instabilities when its frequency is close to...     

时间矢量推进方法及其在叶轮机非定常流分析中的应用

为提高周期性非定常流动的求解效率,将非定常计算的初值问题转换为边值问题,提出了时间矢量推进方法,并将该方法应用于叶轮机多排的非定常流动分析中。通过对两排对转风扇进行非定常仿真,并对比双时间步计算方法的计算结果,讨论了新方法的计算效率,研究了该方法对排间干扰捕捉的准确性和可靠性。得到了以下结论:在物理时间步长相等的情况下,新方法与双时间步方法的计算结果基本一致,且计算时间约为双时间步方法的1/8;时间矢量推进方法能够很好捕捉排间的势扰动、熵扰动和涡扰动以及主流和扰动之间的非线性作用;时刻样本数较少会使时间矢量推进方法捕捉到的非定常变化幅值变小,且无法解析时间尺度较小的非定常流动现象。     

Use of idempotent matrices to validate linear systems software

In seeking to verify various computer implementations of Kalman filters, the extended Kalman filter (EKF), or other algorithms that rely on the same fundamental computations in a variety of different applications, it is useful to first validate software performance using low-dimensional test problems of known solution. Besides reporting the state-of-the-art in computing the critical fundamental linear system building blocks in a simple manner that is easy to understand, the author describes the easy construction of nontrivial test cases of known solution, provides a rigorous demonstration of how to augment/concatenate several low-dimensional test problems of known solution to comprise a higher-dimensional system of known solution that is also to be used in software test and validation/verification, and presents the computation of a closed-form exact optimal control solution that can also be used to validate software     

基于流水避石原理的无人机三维航路规划方法

借鉴自然界流水避石现象,提出一种基于流体计算的无人机(UAV)三维(3D)航路规划方法.首先介绍了球心位于坐标原点时,球形障碍三维绕流问题的解析解.之后采用旋转平移矩阵与流线数据叠加方法生成了任意位置多障碍同时存在的三维流线.为验证解析解的有效性同时给出该方法基于数值模拟的计算过程,对适合无人机三维航路规划的流体模型和数值求解方法进行了分析,并给出了通过数值模拟求解航路的方法.最后,根据无人机机动约束对流线进行处理得到可飞航路,将航路长度、纵向和横侧向机动次数作为子目标函数对航路进行综合评价.仿真结果表明:解析法航路规划中,圆球障碍的地形建模简单计算量小,航路集中在由起点至终点的航路带间;数值法航路规划适合障碍分布复杂的地形,航路分布于规划空间中.这两种方法的航路平滑,能够满足无人机飞行约束,航路具有绕流意义的最优性,可以避免势场法的局部极小问题,并且可以提供多条备选航路.     

Computational prediction of airfoil dynamic stall

The term dynamic stall refers to unsteady flow separation occurring on aerodynamic bodies, such as airfoils and wings, which execute an unsteady motion. The prediction of dynamic stall is important for flight vehicle, turbomachinery, and wind turbine applications. Due to the complicated flow physics of the dynamic stall phenomenon the industry has been forced to use empirical methods for its prediction. However, recent progress in computational methods and the tremendous increase in computing power has made possible the use of the full fluid dynamic governing equations for dynamic stall investigation and prediction in the design process. It is the objective of this review to present the major approaches and results obtained in recent years and to point out existing deficiencies and possibilities for improvements. To this end, potential flow, boundary layer, viscous–inviscid interaction, and Navier–Stokes methods are described. The most commonly used numerical schemes for their solution are briefly described. Turbulence models used for the computation of high Reynolds number turbulent flows, which are of primary interest to industry, are presented. The impact of transition from laminar to turbulent flow on the dynamic stall phenomenon is discussed and currently available methods for its prediction are summarized. The main computational results obtained for airfoil and wing dynamic stall and comparisons with available experimental measurements are presented. The review concludes with a discussion of existing deficiencies and possibilities for future improvements.