利用10N推力器羽流试验数据建立羽流场数学模型

利用MBB10N推力器羽流试验数据建立推力器羽流场的数学模型并确定其模型参数,以便利用此数学模型分析此类推力器对卫星的羽流干扰力、干扰力矩以及对太阳翼、敏感器的热效应等羽流污染。本文建立的羽流场数学模型不同于Simons羽流场数学模型及羽流特征线方法,但本质上仍满足羽流远流场为自由分子流的假设条件;本文建立的羽流场数学模型的非线性表达式更便于利用试验数据实现系统辨识,而且可达到相当满意的辨识准度。     

基于随机振动试验的模态参数辨识

文章介绍了利用随机振动的试验数据进行模态参数辨识的方法。先从理论上证明了从响应数据推导出的传递特性函数可以代替传统的传递函数求出脉冲响应函数,从而直接利用最小二乘复指数法进行模态参数辨识;然后以桁架结构为例,通过随机振动试验数据求得模态参数,并与模态试验的结果相比较,证明该方法的可行性。     

Experimental investigation on a cavity-step-actuated supersonic oscillating jet

Wind tunnel testing is conducted at different back pressures in a vacuum-type wind tun-nel for a novel supersonic fluidic oscillator which consists of a two-dimensional Laval nozzle, a rect-angular cavity and a backward step, to obtain its characteristics and the conditions for jet oscillating. The experimental results show that periodic asymmetrical flipping of the supersonic jet appears over certain nozzle pressure ratio (NPR) range according to schlieren visualization and pressure fluctuations. The jet flipping appears only when the jet is over expanded. The normal-ized average amplitude of the lateral pressure difference acting on the roofs of the cavity and the step varies around 0.2 while the periodic flipping appears. The supersonic jet periodic flipping fre-quencies obtained from the experiments agree well with those from the modified Rossiter mode for cavity-step acoustic resonance, but further investigations are needed to discover the underlying mechanism for the jet flipping.     

Experiment on a Double-Foot Stepping Piezoelectric Linear Motor

A novel double-foot piezoelectric linear motor is proposed.The kinematic model of the motor under stepping motion is presented.The motor mainly consists of a stator with four piezoelectric stacks,a mover,a holding mechanism,and a preloading mechanism to achieve large stroke with high resolution.Finite element simulations are carried out to analyze the motion characteristics of the motor.A prototype is fabricated and a serial experiments are conducted to validate the feasibility of the motor principle.Experimental results indicate that the motor can move at a speed of 670.22μm/s with a driving frequency of 120 Hz and a voltage of 120 V.The resolution of the proposed motor is 3.6μm while the resolution of the single-step motion is 0.1μm.     

Analysis of precipitable water vapour characteristics from GNSS measurements during the snow season in Liaoning Province,China

Global Navigation Satellite System (GNSS) remote sensing precipitable water vapour (PWV) data from November 2015 to March 2019 were combined with snowfall observation data and used to analyse PWV characteristics in Liaoning Province during the snow season (from November to March the following year) and their relationship with snowfall. The potential of using GNSS for PWV measurements was demonstrated using sounding data with a correlation coefficient higher than 0.9 and a mean bias error lower than 0.5 mm. According to the GNSS PWV data gathered at 30-min intervals from 68 GNSS stations in Liaoning during the snow season, the monthly PWV average was highest in November and lowest in January. Negative correlations were found between PWV and altitude. Most of the water vapour was concentrated in the low layer of the atmosphere, and the contribution of this vapour to the PWV was higher during the snow season than in summer. A total of 43 snow cases were identified using the snowfall records from 53 GNSS stations, and the characteristics of PWV during these snowfalls were analysed. An increase in PWV was observed before snowfall events. Moreover, the influence of synoptic systems and air mass origins on PWV was analysed based on National Centers for Environmental Prediction (NCEP) reanalysis data and the Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model. The results show that the water vapour condition was better when the synoptic systems or air masses came from areas south of Liaoning.     

基于支持向量回归代理模型的气动力优化设计

目前,气动力优化设计中通常基于经验风险最小化原则构建代理模型,预测精度的提高需要更多的训练样本,计算代价较大,同时盲目降低代理模型的训练误差难以避免过学习问题。针对上述问题,首先提出采用支持向量回归(SVR)方法基于结构风险最小化原则构建代理模型的思路,然后对测试函数和翼型阻力进行预测,最后对某型运输机机翼进行优化设计试验。结果表明:与其他代理模型对比,基于SVR的代理模型在小样本情况下具有较好的泛化能力,并且能够快速准确地预测气动特性,在飞机优化设计中,可以提高工作效率,优化结果可靠、可控。     

高阶精度方法下的湍流生成项对跨声速流动数值模拟的影响研究

利用五阶空间离散精度的WCNS格式和多块结构网格技术,通过求解雷诺平均NS方程,开展了SST两方程模型不同湍流生成项组合方式对跨声速流动数值模拟影响的计算分析。研究的主要目的是为高阶精度格式在复杂外形上的工程应用提供技术支撑。计算模型采用了RAE2822超临界翼型和DLR-F6翼身组合体构型。研究内容主要包括不同湍流生成项对残差收敛历程、边界层湍流粘性系数分布、边界层速度分布、压力系数分布以及模型整体气动力特性的影响。不同湍流生成项组合方式的流场计算结果还与风洞试验数据进行了对比。研究结果表明:对于小迎角不存在明显分离的跨声速流动,不同湍流生成项对流场的高精度计算结果的影响很小,可以不用考虑。     

基于智能机械臂的任意扫描曲面天线测试系统

传统的天线测试技术已趋成熟,这些系统主要由扫描架与转台构成,体量大且造价相对高昂.而随着人工智能技术和制造水平的巨幅提升,机械臂产业已得到广泛应用,利用高精度机械臂代替扫描架与伺服控制,加之数据后处理算法,开创了天线测试领域的新纪元.研究的基于智能机械臂的任意曲面天线测试系统为国内天线测试领域的首例实践,可实现任意扫描...     

压力对Fe_（16）N_2结构和磁性的影响

用基于密度泛函理论的第一性原理方法,系统地研究了压力对Fe16N2体系结构和磁性的影响。结果表明仅仅离N位最远的Fe Ⅲ拥有一个约为2.84μB的大磁矩,而FeⅠ和Fe Ⅱ原子没有大磁矩产生。此外,还发现从0到47 GPa,总磁矩和单胞体积随着压力的增加单调减小,然而,在48 GPa的压力作用下,伴随着单胞体积的剧减,体系总磁矩消失。     

多层隔热组件的制作工艺

介绍了多层隔热组件及影响其隔热性能的主要因素,包括反射屏与间隔层的选材、多层组件的层密度、放气孔等.结合实际工程应用,对于多层隔热组件的材料选择和制作工艺进行了着重说明.