论加速可靠性增长试验 (Ⅶ )步进应力试验方案的统计分析

对幂律-线性化模型步进应力加速可靠性增长试验方案，给出了模型参数，加速系数及MTBF的极大似然估计，极大后验估计，Bayes估计及其计算方法，对这些方案给出了Monte Carlo模拟方法，并用数值例说明了这些方法。     

转子越过临界转速的振动特性试验研究

以盘偏置单盘双简支试验器转子为对象,由加速与减速的幅频特性曲线确定转子的临界转速。以幅频特性曲线模态计算法确定盘处的偏心距和阻尼比,用弯、扭耦合传递矩阵法计算临界转速及稳态不平衡响应,同时分析了偏心距及初始弯曲按一阶振型分配时,转子越过临界之振动特性。由试验与理论分析结果表明,加速度对振动特性有明显的影响。     

飞行加速度对固体火箭发动机前封头绝热层烧蚀特性影响研究

对固体火箭发动机前封头绝热层在加速度环境的炭化烧蚀特性进行了实验研究,研制了烧蚀试验发动机及相应的离心试验台,用ＮＢＲ,ＥＰＤＭ绝热层模拟实际烧蚀环境进行了不同轴向加速度条件下的烧蚀试验,得到了飞行速度对绝热层炭化烧蚀率影响规律和经验关系式。     

改善双轴发动机加速性的变喷管调节分析

基于发动机各部件特性,应用流动参数变化热容计算方法对某型双轴发动机加速过程进行了数值分析。发展了一种双层迭代方法,成功地模拟了变喷管喉道面积对发动机加速性的影响,并初步给出了改善发动机加速性的变喷管调节方案。     

阳极电流和屏栅电压对5kW离子推力器性能的影响

为了研究5kW离子推力器功率宽范围工作能力,采用试验的方法得到阳极电流和屏栅电压与其性能的影响关系。研究结果表明：离子束流随阳极电流增大呈线性增大。当屏栅电压增加时,推力器离子束流先增加然后趋于稳定,加速栅电流单调减小。推力随功率增大呈线性增长,比冲随功率的增大呈非线性增长,在功率308W~4813W下实现了推力12mN~184mN,比冲1817s~3538s, 效率34%~67%的宽范围调节。同时推力器效率随功率增大逐渐增大,并在2902W时存在明显拐点,在实际在轨应用中要根据任务需求确定最佳工作区间提高推力器性能和效率。     

一种直升机涡轴发动机加速自适应控制研究

提出一种直升机涡轴发动机加速自适应控制方案,它是在ＮＧＧ／ｐ＊２ＰＩＤ控制的基础上加自适应控制律。当发动机性能老化或损伤时,加速时可能引起压气机喘振,这种自适应加速控制方案能适应对象这种性能变化,自动调整方案以消除加速过程出现的喘振现象。这种加速控制比传统的ｗｆ／ｐ＊２开环加速控制具有较高的控制精度,也具有类似高度补偿和喘振恢复项ｐ＊２。这种自适应加速控制只需对原有ＦＡＤＥＣ控制的硬件稍作修改,主要依靠微机控制软件修改就可以将ＦＡＤＥＣ控制提高到自适应控制水平。     

Three-dimensional cooperative guidance strategy and guidance law for intercepting highly maneuvering target

Cooperative interception of the target with strong maneuverability by multiple missiles with weak maneuverability in the three-dimensional nonlinear model is studied. Firstly, the three-dimensional nonlinear model of cooperative guidance is established. The three-dimensional reachable region is represented composed of lateral acceleration and longitudinal acceleration in the two-dimensional coordinate system. Secondly, the problem of the multiple missile's reachable coverage area is transformed into the problem of cooperative coverage. A cooperative coverage strategy is proposed and an algorithm for quickly calculating the number of required missiles is designed. Then, the guidance law based on the cooperative coverage strategy is proposed, and it is proved that cooperative interception of the target can be achieved under the acceleration limit. Moreover, the relations among the number of missiles, the initial array position of terminal guidance and the coverage area of the target’s large maneuver are analyzed. The dynamic adjustment strategy of guidance parameters is proposed to reduce the guidance error. Finally, simulation results show that multiple missiles with low maneuverability can achieve effective interception of target with strong maneuverability through the proposed cooperative strategy and cooperative guidance method.     

天琴一号卫星加速度模式无拖曳控制

结合卫星加速度模式无拖曳控制系统一般组成、各环节典型模型、常见控制器及天琴一号空间惯性基准建立试验卫星的采样周期与控制周期,着眼于工程实际问题的挖掘与解决,重点阐述了该卫星CIC滤波器组频响特性等效、加速度模式无拖曳控制系统稳定裕度及残余加速度指标分析与综合等技术内容。研究表明,多周期离散系统真实稳定裕度难于准确预测;积分系数是决定PSD指标的关键参数;抗混淆滤波器是提升时域残余加速度指标的关键环节,且有利于抑制高频数据在PSD低中频段的高频折叠;在未引入抗混淆滤波器的情形下,频域指标统计应以进入控制器的残余加速度数据为准。在轨飞行试验结果与仿真结果基本吻合。     

Experimental investigation on boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels subjected to an acceleration force

Experiments were carried out to investigate the boiling heat transfer characteristics of Al_2O_3-water nanofluids in swirl microchannels under terrestrial gravity and acceleration fields. A centrifuge with a two-meter long rotational arm was used to simulate the acceleration magnitude up to 9 g and three various acceleration directions. Three test sections with different geometric parameters were applied. The volume concentration of Al_2O_3 nanoparticles with an average diameter of 13 nm was varied from 0.07% to 0.1%. The mass flow rate and vapor quality were in ranges of 3–6 kg/h and 0.4–1.0%, respectively. The effects of the mass flow rate, microchannel aspect ratio,vapor quality, nanoparticle volume concentration, and acceleration direction and magnitude were analyzed in a systematic manner. Experimental results showed that the acceleration direction and magnitude had significant influences on the boiling heat transfer. The heat transfer under configuration C was found to be superior to that under configurations A and B. Moreover, the heat transfer coefficient increased with increases of the mass flow rate and the volume concentration and decreased with the aspect ratio.     

Finding the suitable drag-free acceleration noise level for future low-low satellite-to-satellite tracking geodesy missions

This paper evaluates the impact of residual acceleration noise on the estimation of the Earth’s time-varying gravity field for future low-low satellite-to-satellite tracking missions. The goal is to determine the maximum level of residual acceleration noise that does not adversely affect the estimation error. The Gravity Recovery And Climate Experiment (GRACE) has provided monthly average gravity field solutions in spherical harmonic coefficients for more than a decade. It provides information about land and ocean mass variations with a spatial resolution of ～350?km and with an accuracy within 2?cm throughout the entire Earth. GRACE Follow-on was launched in May 2018 to advance the work of GRACE and to test a new laser ranging interferometer, which measures the range between the two satellites with higher precision than the K-Band ranging system used in GRACE. Moreover, there have been simulation studies that show, an additional pair of satellites in an inclined orbit increases the sampling frequency and reduces temporal aliasing errors. Given the fact that future missions will likely continue to use the low-low satellite-to-satellite tracking formation with laser ranging interferometry, it is expected that the residual acceleration noise will become one of the largest error contributor for the time-variable gravity field solution. We evaluate three different levels of residual acceleration noise based on demonstrated drag-free systems to find a suitable drag-free performance target for upcoming geodesy missions. We analyze both a single collinear polar pair and the optimal double collinear pair of drag-free satellites and assume the use of a laser ranging interferometer. A partitioned best linear unbiased estimator that was developed, incorporating several novel features from the ground up is used to compute the solutions in terms of spherical harmonics. It was found that the suitable residual acceleration noise level is around 2?×?10^?12?ms^?2?Hz^?1/2. Decreasing the acceleration noise below this level did not result in more accurate gravity field solutions for the chosen mission architecture.