Supersonic Two-Dimensional Minimum Length Nozzle Design at High Temperature. Application for Air

When the stagnation temperature of a perfect gas increases, the specific heat ratio does not remain constant any more, and start to vary with this temperature. The gas remains perfect, its state equation remains always valid, except it will name in more calorically im-perfect gas or gas at High Temperature. The goal of this work is to trace the profiles of the supersonic Minimum Length Nozzle with centered expansion when the stagnation temperature is taken into account, lower than the threshold of dissociation of the molecules and to have for each exit Mach number several nozzles shapes by changing the value of the temperature. The method of characteristics is used with a new form of the Prandtl Meyer function at high temperature. The resolution of the obtained equations is done by the second order of finite differences method by using the predictor corrector algorithm. A study on the error given by the perfect gas model com-pared to our model is presented. The comparison is made with a calorically perfect gas for goal to give a limit of application of this model. The application is for the air.     

模拟过载条件下燃烧室凝相颗粒形态参数试验研究

通过地面模拟过载粒子收集试验装置,完成了推进剂在3种不同压强工况下的粒子收集试验,初步获得了粒度分布特性、微观形貌特性及成分分布等形态参数。研究结果表明,粒子中径分布明显高于非过载状态,5.6~11.5 MPa范围内,d(0.5)主要分布在120~190μm之间。同时,针对某飞行试验发动机残骸故障处残留凝相粒子进行了收集与分析,并与地面同种压强状态下粒子形态参数进行了对比,两者分布较为一致,均呈双峰分布,粒子d(0.5)约为100~130μm。     

一种基于归一化参数的蠕变模型

针对传统蠕变模型(如Norton律)不能模拟蠕变第3阶段的不足,提出了一种基于归一化参数的蠕变模型,该模型以归一化时间为变量,以归一化应力和归一化温度为参数,可完整描述蠕变曲线的所有3个阶段.在该模型的基础上提出了能更好地描述蠕变曲线第1阶段的改进形式.利用所发展的模型对直接时效GH4169G材料的蠕变试验曲线3个阶段进行了较好地模拟,验证了该模型的描述蠕变变形的能力;同时确立了所发展模型中各参数与归一化温度和归一化应力之间的函数关系,取得了较好的效果;并且能与有限元软件结合,表明所发展的模型可应用于实际结构的蠕变分析.      

Gaussian process regression model incorporated with tool wear mechanism

Cutting tool condition directly affects machining quality and efficiency. In order to avoid severely worn tools used during machining process and fully release the remaining useful life in the meanwhile, a reliable evaluation method of remaining useful life of cutting tools is quite necessary.Due to the variation of cutting conditions, it is a challenge to predict remaining useful life of cutting tools by a unified model. In order to address this issue, this paper proposes a method for predictin...     

GH3625合金激光直接成形工艺

为了研究工艺参数对金属激光直接成形零件质量的影响,通过正交试验的方法对单道单层GH3625合金激光直接成形工艺进行了研究,主要探究了激光功率、扫描速度、送粉速度等参数对单道单层成形截面宽度和高度的影响规律,提出预测模型并做了验证。结果表明,在单道单层成形中,激光功率、送粉速度、扫描速度等工艺参数对单道宽度和高度具有不同程度的影响,其中,对于单道成形宽度和高度来讲,扫描速度对其影响最为明显。试验验证结果表明借助Minitab软件得到的线性回归模型是有效的。     

GH4169车削过程的热力耦合作用及残余应力场研究

镍基高温合金GH4169是一种拥有优良的机械性能及抗腐蚀能力的耐热合金,被广泛应用于航空航天工程等领域,其切削过程因热力耦合作用产生的残余应力对零件的疲劳性能有重要影响.本文采用GH4169车削试验及Deform-3D仿真模拟相结合的方法,通过试验的切削力和仿真的温度-应变场对残余应力场的形成机理进行研究.结果表明:刀具磨损对主切削分力和车削温度的影响非常显著,在刀片磨钝过程中,主切削分力由538N增大到756N,剪切区温度由552℃增高到654℃,工件表面的应变由3.3升高到3.5;刀具磨损导致切削力和的温度-应变的增大,致使表面圆周和进给方向的残余拉应力峰值由517MPa、242MPa增大到860MPa、442MPa;表层残余压应力峰值-696MPa、-356MPa增大到-756MPa、-456MPa;残余应力层深度由72μm增大到85μm.     

Proposal of new models of the bottom-side B0 and B1 parameters for IRI

The time series of hourly electron density profiles N(h) obtained from 27 ionosonde stations distributed world-wide have been used to obtain N(h) average profiles on a monthly basis and to extract the expected bottom-side parameters that define the IRI profile under quiet conditions. The time series embrace the time interval from 1998 to 2006, which practically contains the entire solar cycle 23. The Spherical Harmonic Analysis (SHA) has been used as an analytical technique for modeling globally the B0 and B1 parameters as general functions on a spherical surface. Due to the irregular longitudinal distribution of the stations over the globe, it has been assumed that the ionosphere remains approximately constant in form for a given day under quiet conditions for a particular coordinate system. Since the Earth rotates under a Sun-fixed system, the time differences have been considered to be equivalent to longitude differences. The time dependence has been represented by a two-degree Fourier expansion to model the annual and semiannual variations and the year-by-year analyses of the B0 and B1 have furnished nine sets of spherical harmonic coefficients for each parameter. The spatial–temporal yearly coefficients have been further expressed as linear functions of Rz12 to model the solar cycle dependence. The resultant analytical model provides a tool to predict B0 and B1 at any location distributed among the used range of latitudes (70°N–50°S) and at any time that improves the fit to the observed data with respect to IRI prediction.     

一种基于光纤捷联惯性系统大样本统计的参数有效期评估方法

标定参数有效期是武器系统在使用过程中的一项重要指标,传统方法使用单套惯组的多次测试数据来评估标定参数的有效期。但这种抽测方法存在样本较少、耗时长的缺点。为克服以上问题,提出了一种利用正态分布和卡方检验分析多套惯组的单次测试数据来评估标定参数有效期的方法,样本量大、置信度高。用此评估方法对75套光纤惯组单次的测试数据进行统计分析,结果表明标定参数满足有效期要求,证明了本评估技术的有效性、可行性。同时,还分析了部分标定参数误差的漂移机理,为今后设计出长期稳定性更高的光纤惯组提供了理论支撑。     

冷喷涂工艺参数对TC4涂层性能的影响

为了研究冷喷涂技术在TC4基板上沉积TC4涂层的性能,分析了喷涂气体种类和温度对涂层孔隙率、硬度和粉末利用率的影响规律。采用N_2和He两种气体以及400、500和600℃进行喷涂工艺试验研究。结果表明:在He或者N_2下,温度越高,制备的涂层越致密,涂层硬度越高,粉末利用率也越高;相同气体温度条件下,采用He制备的涂层较N_2更加致密,涂层硬度更高,粉末利用率也较N_2高。采用He、气体温度600℃、喷涂压力0.9 MPa,制备的涂层孔隙率低到0.8%,硬度达到440 HV0.2,硬度相对基体提高33%,粉末利用率高达88.2%。     

工艺管路对节流阀性能参数影响的分析

以火箭发动机零部组件液流试验的挤压式系统为基础,分析和讨论了典型单流路试验系统和双流路试验系统对节流阀各项性能参数的影响,并提出了在目前技术改造项目中,设计自动化液流试验系统时关于节流阀的参数计算及选取原则。