高灵敏度莫尔偏折法及其在激波风洞流场中的应用

本文介绍了一种具有高灵敏度的莫尔偏折法，从理论上分析了其工作和测量原理。并把这种方法用于高超声速激波风洞中流场的显示和测量，获得了几种特殊模型流场的清晰莫尔偏折图，定量计算了高超声速激波风洞中带有凸起物模型三维密度场的分布。     

Analytic estimation and numerical modeling of actively cooled thermal protection systems with nickel alloys

Actively cooled thermal protection system has great influence on the engine of a hypersonic vehicle, and it is significant to obtain the thermal and stress distribution in the system. So an analytic estimation and numerical modeling are performed in this paper to investigate the behavior of an actively cooled thermal protection system. The analytic estimation is based on the electric analogy method and finite element analysis（FEA） is applied to the numerical simulation. Temperature and stress distributions are obtained for the actively cooled channel walls with three kinds of nickel alloys with or with no thermal barrier coating（TBC）. The temperature of the channel wall with coating has no obvious difference from the one with no coating, but the stress with coating on the channel wall is much smaller than that with no coating. Inconel X-750 has the best characteristics among the three Ni-based materials due to its higher thermal conductivity, lower elasticity module and greater allowable stress. Analytic estimation and numerical modeling results are compared with each other and a reasonable agreement is obtained.     

载人月球软着陆任务紧急中止轨道分析与设计

针对载人月球软着陆进程中,由载人飞船发动机失效引起的任务中止问题,首先分析主发动机失效可能引起的撞月轨道、环绕轨道、逃逸轨道等轨道类型及其特点;然后分析了中止任务执行的前提条件及中止过程的导航制导要求,在此基础上,考虑二体模型,提出普适的共面软着陆中止轨道计算方法;最后,在考虑登月飞船生保系统时间限制条件下,给出下降级主发动机失效情况下,撞月轨道的中止仿真算例。仿真结果表明,该方法可以实现登月飞船软着陆制动故障情形下的任务中止,能够确保飞船安全返回环月轨道。     

Extension of the low diffusion particle method for near-continuum two-phase flow simulations

The low diffusion (LD) particle method, proposed by Burt and Boyd, is modified for the near-continuum two-phase flow simulations. The LD method has the advantages of easily coupling with the direct simulation Monte Carlo (DSMC) method for multi-scale flow simulations and dramatically reducing the numerical diffusion error and statistical scatter of the equilibrium particle methods. Liquidor solid-phase particles are introduced in the LD method. Their velocity and temperature updating are respectively, calculated from the motion equation and the temperature equation according to the local gas properties. Coupling effects from condensed phase to gas phase are modeled as momentum and energy sources, which are respectively, equal to the negative values of the total momentum and energy increase in liquid or solid phase. The modified method is compared with theoretical results for unsteady flows, and good agreements are obtained to indicate the reliability of the one-way gas-to-particle coupling models. Hybrid LD-DSMC algorithm is implemented and performed for nozzle discharging gas-liquid flow to show the prospect of the LD-DSMC scheme for multi-scale two-phase flow simulations.     

FM73M 胶膜及其与PMI 泡沫芯的胶接机理

采用DSC研究了不同升温速率下FM73M胶膜的固化反应特性,根据DSC曲线得到了胶膜的凝胶化温度和固化温度等工艺参数,建立了其固化动力学模型,确定胶膜的固化参数为(125±2)℃/90min.在此基础上,通过SEM研究了胶膜在PMI泡沫芯材内的分布以及界面结合状况(界面润温情况、气孔、缺陷),分析了胶膜与泡沫芯的胶接机理.     

复合材料螺栓连接失效的数值模拟

作为一种重要的连接及承载形式,复合材料螺栓的连接性能直接影响到结构组件的承载可靠性.本文针对复合材料各向异性及渐进损伤特点,建立了包含复合材料螺栓及复合材料板的有限元模型.通过编制U-Mat程序,利用ABAQUS商用软件对复合材科螺栓连接的失效过程进行了数值模拟,得到了连接件的载荷-位移曲线,并对连接件的失效模式进行了分析.     

Non-destructive Evaluation of Absolute Stress in Steel Members Using Shear-Wave Spectroscopy

Non-destructive measurement of absolute stress in steel members can provide useful information to optimize the design of steel structures and allow the safety of existing structures to be evaluated.This paper investigates the non-destructive capability of ultrasonic shear-wave spectroscopy in absolute stress evaluation of steel members.The effect of steel-member stress on the shear-wave amplitude spectrum is investigated,and a method of absolute stress measurement is proposed.Specifically,the process for evaluating absolute stress using shear-wave spectroscopy is summarized.Two steel members are employed to investigate the relationship between the stress and the frequency in shear-wave echo amplitude spectrum.The H-beam loaded by the universal testing machine is evaluated by the proposed method and the traditional strain gauge method for verification.The results show that the proposed method is effective and accurate for determining absolute stress in steel members.     

Inertial aided BDS triple-frequency integer ambiguity rounding method

The integer ambiguity resolution (AR) of carrier phase is significant for Global Navigation Satellite System (GNSS) precise positioning. However, in kinematic case, single-epoch AR methods based on alone GNSS are usually not reliable due to the instable pseudorange accuracy. Moreover, the computation of classical AR method Least Squares Ambiguity Decorrelation Adjustment (LAMBDA) is large. Thus, the inertial measurement unit (IMU) is introduced, a new inertial-aided AR method that directly rounds the float ambiguity of BeiDou triple-frequency combined observations, which is characterized by long wavelength, low carrier-phase noise and ionospheric delay, is proposed. The mathematical model of the new method is derived first. Then the impacts of the carrier-phase noise, ionospheric delay and inertial navigation system (INS) position error on the AR success ratio of combined observation are analyzed through probabilistic approach. Based on above investigation, the combinations (0, ?1, 1), (1, 4, ?5) and (4, ?2, ?3) are selected to resolve the original ambiguity. A vehicular integrated navigation test is performed to demonstrate the proposed method. The results show that the average AR success ratios of the three selected combinations, whose float ambiguity errors are 0.041, 0.146, 0.279 cycle respectively, are above 97.25% without regard to low-elevation C05. With respect to positioning accuracy based on our AR method when compared with IE software, the east, north, up error RMS of position are 0.042, 0.024, 0.069 m, respectively. In terms of the AR recover after the BeiDou signals outage, as long as 62 s BeiDou signal complete outage, all the ambiguities of all satellites could be re-fixed immediately. Besides, during the 90 s signals partial outage, the AR is not influenced by the position error, since the float ambiguity errors are all below half-cycle. The research of this contribution demonstrates the effectiveness of the proposed new method, which indicates it is applicable to kinematic positioning, even in BDS degraded and denied environments.     

风云二号卫星地面控制系统自适应同步控制方法

针对风云二号07星测控实施过程中部分姿章联控参数未能正常执行的系统间时序控制不同步问题,研究提出一种地面控制系统自适应同步控制方法,分析卫星历史数据得到有效接收时间区间,取所有有效接收时间区间的交集得到最终有效接收时间区间。经验证,方法可有效解决系统间时序不同步的问题,精度高,控制效果好。