基于层流小火焰和beta-PDF的预混燃烧模型

研究了基于层流小火焰概念和假定beta-PDF(probability density function)的湍流预混燃烧模型.该模型采用PREMIX程序来计算层流小火焰,将计算结果表示为进程变量的函数,并利用进程变量的beta-PDF积分生成了用于RANS(雷诺平均Navier-Stokes)计算的PDF表.以化学当量的甲烷湍流本生火焰为算例对模型进行了计算验证,并与Zimont模型的计算结果和实验结果做了对比.结果表明,平均速度分布与实验符合的较好,温度和湍动能计算结果有待改善.本模型高估了化学反应速率,导致计算火焰比实际瘦,这是因为模型中未能考虑湍流对火焰的拉伸和弯曲效应,考虑湍流拉伸和弯曲效应的预混燃烧模型是今后进一步研究的方向.      

混合变量系统基于MCMC的自适应重要抽样法

 系统关键故障的发生,会导致系统处于各种离散性能降级状态.针对传统的基于马尔可夫链蒙特卡罗(Markov chain Monte Carlo,MCMC)的自适应重要抽样法只适用于连续变量系统的不足,提出考虑混合变量的基于MCMC的自适应重要抽样法,以支持系统性能可靠性的高效仿真.该方法首先将由关键故障产生的不同失效域组成失效空间,并通过初始样本点在失效空间中随机游走构造马尔可夫链模拟样本;然后综合考虑连续变量与离散变量,利用核密度估计构建混合核抽样密度函数;再根据该密度函数进行重要抽样仿真并计算系统的性能可靠性;最后对该方法的仿真效率进行理论分析.通过电液舵机(Electro-Hydrostatic Actuator,EHA)案例对方法的正确性和仿真效率进行验证.     

复合材料质量烧蚀率计算模型实验研究

通过对CF/S- 157PF复合材料进行氧-乙炔烧蚀试验研究,得到了质量烧蚀率,并利用多元线性回归方法,拟合得到了该参数与热流密度和烧蚀时间的数学模型,即M=0.043.q0.128·t-0.191.经检验,该回归模型适用性较好,预测精度较高,为复合材料该项烧蚀性能的评估建立了快速、有效、可靠的试验方法.     

爆轰胞格尺寸的统计分析

爆轰胞格尺寸作为可燃系统的本征值,可用来确定爆轰传播时的临界尺寸,比如直管传播时的临界管径、管道突扩时的临界尺寸等.然而,该尺寸的测量具有较强的主观性.为了减少人工测量带来的不确定性,文章采用两种统计方法:概率密度函数法和自相关函数法,对数值模拟得到的不同规则程度的爆轰胞格进行了统计分析.爆轰胞格的不规则程度采用单步反...     

用差分法处理相关性测量数据方法探讨

当测量参数（或称测量元素）具有强相关性时,运用测量求差法解算测量结果,能消除相关性误差因素的影响,获得高精度测量结果,如电影望远镜同帧画幅测量脱靶量.基于此,运用测量方法和数学手段构建一个虚拟的元素相关测量系统,以消除相关性误差因素的影响,同样能获得理想结果.用多台测速雷达组成的系统,可使火炮弹丸空间坐标的测量精度达到毫米量级,从而满足多种火炮立靶密集度的测量精度要求.     

扇形叶栅通道中密度比和流量比对叶片表面全气膜冷却特性的影响

为了研究扇形通道中真实三维弯扭导向叶片全气膜冷却特性,本文采用压敏漆(PSP)测试技术实验测量了叶片全气膜冷却效率,获得了不同密度比(1、1.5)和质量流量比(9.71%、11.64%、12.47%)对叶片全气膜冷却效率的影响规律,结果表明：低密度比条件下,随着出流比增加,叶片压力面侧气膜冷却效率逐渐增加,叶片吸力面侧靠近前缘区域气膜孔下游的冷却效率减小；密度比增加可以使叶片整体气膜冷却效率提高,其中压力面前侧靠近前缘区域的冷却效率提高最为明显,最多提高了182%；高密度比条件下,增加出流比仅会使得压力面侧-0.8< S/C <0气膜冷却效率小幅度增加。     

A Partially Orthogonal EnKF approach to atmospheric density estimation using orbital debris

A key requirement for accurate trajectory prediction and space situational awareness is knowledge of how non-conservative forces affect space object motion. These forces vary temporally and spatially, and are driven by the underlying behavior of space weather particularly in Low Earth Orbit (LEO). Existing trajectory prediction algorithms adjust space weather models based on calibration satellite observations. However, lack of sufficient data and mismodeling of non-conservative forces cause inaccuracies in space object motion prediction, especially for uncontrolled debris objects. The uncontrolled nature of debris objects makes them particularly sensitive to the variations in space weather. Our research takes advantage of this behavior by utilizing observations of debris objects to infer the space environment parameters influencing their motion.The hypothesis of this research is that it is possible to utilize debris objects as passive, indirect sensors of the space environment. We focus on estimating atmospheric density and its spatial variability to allow for more precise prediction of LEO object motion. The estimated density is parameterized as a grid of values, distributed by latitude and local sidereal time over a spherical shell encompassing Earth at a fixed altitude of 400 km. The position and velocity of each debris object are also estimated. A Partially Orthogonal Ensemble Kalman Filter (POEnKF) is used for assimilation of space object measurements to estimate density.For performance comparison, the scenario characteristics (number of objects, measurement cadence, etc.) are based on a sensor tasking campaign executed for the High Accuracy Satellite Drag Model project. The POEnKF analysis details spatial comparisons between the true and estimated density fields, and quantifies the improved accuracy in debris object motion predictions due to more accurate drag force models from density estimates. It is shown that there is an advantage to utilizing multiple debris objects instead of just one object. Although the work presented here explores the POEnKF performance when using information from only 16 debris objects, the research vision is to utilize information from all routinely observed debris objects. Overall, the filter demonstrates the ability to estimate density to within a threshold of accuracy dependent on measurement/sensor error. In the case of a geomagnetic storm, the filter is able to track the storm and provide more accurate density estimates than would be achieved using a simple exponential atmospheric density model or MSIS Atmospheric Model (when calm conditions are assumed).     

微小卫星热控关键技术研究

介绍了国内外微小卫星的现状与发展趋势。针对微小卫星高功率密度和低热惯性给热控设计带来的新问题,讨论了微小卫星的热控制技术,提出了新的设计理念和方法。文章认为,必需尽快研发微机电技术,如何小型化、轻量化、智能化解决散热问题是微小卫星热控制的关键所在。     

激光选区熔化成形SiCP/AlSi10Mg复合材料工艺及性能研究

为研究激光选区熔化(SLM)成形技术制备SiC颗粒增强AlSi10Mg复合材料的成形机理,开展了SLM成形工艺参数(扫描间距、扫描速度)对致密度、机械性能等影响情况的研究。结果表明:所制备试样中SiC增强颗粒分布均匀,并与基体具有连续相容的冶金结合界面。当激光扫描速度从900 mm/s升高到2 100 mm/s时,在不同的扫描间距下,复合材料试样致密度均随之降低;当扫描间距在0.09～0.12 mm内变化时,在不同的扫描速度下,致密度变化趋势并不一致;在激光功率490 W、铺粉层厚0.04 mm、扫描间距0.12 mm、扫描速度900 mm/s时,制备的SiC颗粒增强AlSi10Mg复合材料试样得到最佳综合性能(相对密度99.1%,显微硬度198.7 HV0.2,抗拉强度341.9 MPa);在该最佳工艺参数下,成功制备出复杂结构的薄壁零件。研究为SLM成形SiCP/AlSi10Mg复合材料在航空航天和空间领域的应用提供了理论基础和实验依据。